Protection and control of wireless power systems

ABSTRACT

One general aspect includes methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for fault protection of a bidirectional wireless power transfer system. The method includes the actions of detecting, by control circuitry of a wireless power transfer device, a fault for the bidirectional wireless power transfer system. Identifying an operating personality of the wireless power transfer device and a hardware configuration of the wireless power transfer device. Identifying, in response to detecting the fault and based on the operating personality and the hardware configuration, protection operations for protecting the wireless power transfer device from the fault. Controlling operations of the wireless power transfer device according to the protection operations. Other implementations of this aspect include corresponding systems, circuitry, controllers, apparatus, and computer programs, configured to perform the actions of the methods, encoded on computer storage devices.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of and claims priority under 35U.S.C. § 120 to U.S. patent application Ser. No. 16/024,045, filed onJun. 29, 2018, which claims the benefit of U.S. Provisional PatentApplication Nos. 62/526,842, filed on Jun. 29, 2017; 62/608,052, filedon Dec. 20, 2017; 62/662,148, filed on Apr. 24, 2018; 62/662,462, filedon Apr. 25, 2018; and 62/662,486 filed on Apr. 25, 2018. The entirecontents of each of these priority applications are incorporated hereinby reference.

TECHNICAL FIELD

The disclosure generally relates to wireless power systems and, moreparticularly, the disclosure relates to protection and sensors forwireless power systems.

BACKGROUND

Wireless power systems employ tunable impedance matching circuits toefficiently transmit power to a coupled load. The behavior of the loadmay be outside the control of the wireless power system and may thuscause undesirable conditions in the components of the wireless powersystem, leading to dangerous operation and possible damage.

SUMMARY

In general, the disclosure features control and protection systems foruni-directional and bidirectional wireless power transfer systems. Thedevices and process described herein can be used in a variety ofcontexts, including implantable devices, cell phone and other mobilecomputing device chargers, and chargers for electric vehicles.

In a first general aspect, the disclosure features, a sensor network fora wireless power transfer system. The sensor network includes adifferential voltage sensing circuit and a current sensing circuit. Thedifferential voltage sensing circuit is arranged within a wireless powertransfer system to measure a rate of change of a voltage differencebetween portions of an impedance matching network and generate a firstsignal representing the rate of change of the voltage difference. Thecurrent sensing circuit is coupled to the differential voltage sensingcircuit and configured to calculate, based on the first signal, acurrent through a resonator coil coupled to the wireless power transfersystem.

In a second general aspect, the disclosure features a wireless powertransfer system that includes a resonator coil, an impedance matchingnetwork coupled to the resonator coil, and a sensor network. The sensornetwork includes a differential voltage sensing circuit and a currentsensing circuit. The differential voltage sensing circuit is arranged tomeasure a rate of change of a voltage difference between portions of theimpedance matching network and generate a first signal representing therate of change of the voltage difference. The current sensing circuit iscoupled to the differential voltage sensing circuit and configured tocalculate, based on the first signal, a current through the resonatorcoil.

These and the following aspects can each optionally include one or moreof the following features.

In some implementations, the differential voltage sensing circuit isconfigured to scale the first signal in response to a second signal, thesecond signal representing a current through the impedance matchingnetwork.

In some implementations, the portions of the impedance matching networkare tunable matching networks that include one or more tunablecapacitors.

In some implementations, the differential voltage sensing circuitincludes an amplification stage having a unity gain amplifier. In someimplementations, the unity gain amplifier is configured to provide thefirst signal as a single-ended voltage signal. In some implementations,the differential voltage sensing circuit is arranged to apply a secondsignal to the unity gain amplifier to scale the first signal in responseto the second signal, the second signal representing a current throughthe impedance matching network.

In some implementations, the differential voltage sensing circuitincludes a differentiator circuit.

In some implementations, the current sensing circuit includes adifferential circuit configured to generate a second signal representingthe current through the resonator coil coupled to the wireless powertransfer system by subtracting the first signal from a second signal,the second signal representing a current through the impedance matchingnetwork.

In a third general aspect, the disclosure features a protection networkfor a wireless power transfer system. The protection network includes adifferential voltage sensing circuit, a first current sensing circuit,and a second current sensing circuit. The differential voltage sensingcircuit is arranged within a wireless power transfer system to measure arate of change of a voltage difference between portions of an impedancematching network and generate a first signal representing the rate ofchange of the voltage difference. The first current sensing circuit isarranged to measure a first current and generate a second signalrepresenting the first current, where the first current is through theimpedance matching network. The second current sensing circuit iscoupled to the differential voltage sensing circuit and to the firstcurrent sensing circuit. The second current sensing circuit isconfigured to calculate, based on the first signal and the secondsignal, a second current and generate a third signal representing thesecond current, where the second current is through a resonator coilcoupled to the wireless power transfer system. This aspect canoptionally include one or more of the following features.

In some implementations, the differential voltage sensing circuit iscoupled to the first current sensing circuit, and wherein thedifferential voltage sensing circuit is configured to scale the firstsignal in response to the second signal.

In some implementations, the differential voltage sensing circuitcomprises an amplification stage includes a unity gain amplifier.

In some implementations, the unity gain amplifier is configured toprovide the first signal as a single-ended voltage signal.

In some implementations, the differential voltage sensing circuit iscoupled to the first current sensing circuit, and wherein thedifferential voltage sensing circuit is arranged to apply the secondsignal to the unity gain amplifier to scale the first signal in responseto the second signal.

In some implementations, the differential voltage sensing circuitcomprises a differentiator circuit. In some implementations, the secondcurrent sensing circuit comprises a differential circuit configured togenerate the third signal by subtracting the first signal from thesecond signal.

Some implementations further include fault protection circuitry coupledto respective output terminals of the first current sensing circuit andthe second current sensing circuit, the fault protection circuitryconfigured to bypass a tunable matching network (TMN) in response to amagnitude of the second signal or a magnitude of the third signalexceeding a respective threshold value.

In some implementations, the fault protection circuitry is furtherconfigured to bypass the tunable matching network by latching a controlsignal for a TMN bypass transistor in an asserted state.

In some implementations, the fault protection circuitry is furtherconfigured to delay latching the control signal until a voltage acrossthe TMN is below a TMN voltage threshold value.

Some implementations further include fault protection circuitry coupledto respective output terminals of the first current sensing circuit andthe second current sensing circuit, the fault protection circuitryconfigured to shutdown an inverter-rectifier in response to a magnitudeof the second signal or a magnitude of the third signal exceeding arespective threshold value.

In a fourth general aspect, the disclosure features a fault protectionmethod for a bidirectional wireless power transfer system. The methodincludes the actions of detecting, by control circuitry of a wirelesspower transfer device, a fault for the bidirectional wireless powertransfer system. Identifying an operating personality of the wirelesspower transfer device and a hardware configuration of the wireless powertransfer device. Identifying, in response to detecting the fault andbased on the operating personality and the hardware configuration,protection operations for protecting the wireless power transfer devicefrom the fault. Controlling operations of the wireless power transferdevice according to the protection operations. Other implementations ofthis aspect include corresponding systems, circuitry, controllers,apparatus, and computer programs, configured to perform the actions ofthe methods, encoded on computer storage devices.

These and other implementations can each optionally include one or moreof the following features.

In some implementations, in response to the operating personalityindicating that the wireless power transfer device is operating as awireless power transmitter, the protection operations include shuttingdown an inverter-rectifier and shorting at least a portion of animpedance matching circuit. In some implementations, shutting down theinverter-rectifier includes overriding inverter-rectifier pulse widthmodulation (PWM) control signals.

In some implementations, in response to the operating personalityindicating that the wireless power transfer device is operating as awireless power receiver and the hardware configuration indicating thatthe wireless power transfer device is configured as a grid-connectedsystem, the protection operations include shutting down aninverter-rectifier, shorting at least a portion of an impedance matchingcircuit to dissipate current from a resonator coil, and switching in aresistor configured to dissipate excess power from theinverter-rectifier. In some implementations, shutting down theinverter-rectifier includes overriding inverter-rectifier pulse widthmodulation (PWM) control signals.

In some implementations, in response to the operating personalityindicating that the wireless power transfer device is operating as awireless power receiver, the protection operations include shutting downan inverter-rectifier, and shorting at least a portion of an impedancematching circuit to dissipate current from a resonator coil.

In some implementations, shutting down the inverter-rectifier includesoverriding inverter-rectifier pulse width modulation (PWM) controlsignals.

In some implementations, in response to the operating personalityindicating that the wireless power transfer device is operating as awireless power receiver and the hardware configuration indicating thatthe wireless power transfer device is configured as a device-connectedsystem, the protection operations include closing switches of aninverter-rectifier to provide a short circuit between terminals of aresonator coil. In some implementations, the protection operations causea corresponding fault condition in a second wireless power transferdevice that is magnetically coupled to the first wireless power transferdevice.

In some implementations, the fault is at least one of: a tunableimpedance matching network fault, an overcurrent fault, or anovervoltage fault.

In some implementations, the fault is an overvoltage fault or anovercurrent fault triggered by a load disconnect.

In some implementations, the method includes initiating the fault bydisconnecting a load from the wireless power transfer device in responseto detecting a vehicle collision.

In a fifth general aspect, the disclosure features a method of operatinga bidirectional wireless power transfer system. The method includes theactions of transmitting, by a first wireless power transfer device to asecond wireless power transfer device, instructions to reverse adirection of power flow between the first wireless power transfer deviceand the second wireless power transfer device. Receiving, from thesecond wireless power transfer device, an indication that the secondwireless power transfer device has reconfigured to operate according areverse direction of power flow. In response to the indication the firstwireless power device assigns an operating personality of the firstwireless power transfer device in accordance with the reverse directionof power flow, and controls operation of an inverter-rectifier of thefirst wireless power transfer device for operation according to theoperating personality. Other implementations of this aspect includecorresponding systems, circuitry, controllers, apparatus, and computerprograms, configured to perform the actions of the methods, encoded oncomputer storage devices.

These and other implementations can each optionally include one or moreof the following features.

In some implementations, the operating personality indicates that thefirst wireless power transfer device is operating as a wireless powertransmitter, and controlling operation of the inverter-rectifierincludes generating pulse width modulation (PWM) control signals foroperating the inverter-rectifier as an inverter.

In some implementations, the operating personality indicates that thefirst wireless power transfer device is operating as a wireless powerreceiver, and controlling operation of the inverter-rectifier includesgenerating pulse width modulation (PWM) control signals for operatingthe inverter-rectifier as a rectifier.

In some implementations, the operating personality indicates that thefirst wireless power transfer device is operating as a wireless powerreceiver, and controlling operation of the inverter-rectifier includesin response to a power at the inverter-rectifier being less than athreshold value, operating the inverter-rectifier in a passive rectifiermode; and in response to the power at the inverter-rectifier beinggreater than the threshold value, generating pulse width modulation(PWM) control signals for operating the inverter-rectifier in an activerectification mode.

In some implementations, the PWM control signals alternately turn oncorresponding pairs of transistors in the inverter-rectifier to generatea DC output signal.

In some implementations, the PWM control signals alternately turn oncorresponding pairs of transistors in the inverter-rectifier in responseto detecting a zero current condition at an input to theinverter-rectifier.

In some implementations, the method includes in response to theindication, resetting a tunable matching network of the first wirelesspower transfer device and controlling operation of the tunable matchingnetwork in accordance with the assigned operating personality.

In some implementations, the first wireless power transfer device iscoupled to a vehicle and the second wireless power transfer device iscoupled to a power grid.

In a sixth general aspect, the disclosure features a method forprotecting a wireless power system during a load disconnect condition inwhich a load is disconnected from an output of a rectifier of a wirelesspower receiver, the wireless power system comprising the wireless powerreceiver and a wireless power transmitter, the wireless power receiverconfigured to receive power from the wireless power transmitter. Themethod includes detecting, by a load disconnect sensor, a loaddisconnect condition. Shorting, by a first controller, two or morerectifier-protection switches, each protection switch coupled to a diodeof the rectifier. Shorting, by a second controller, a firstTMN-protection switch coupled to a receiver-side tunable capacitor, thetunable capacitor coupled to an input of the rectifier. Detecting, by acurrent sensor coupled to the transmitter, an overcurrent condition inan inverter of the transmitter. Shutting off, by a third controller, theinverter. Shorting, by a fourth controller, a second TMN-protectionswitch coupled to a receiver-side tunable capacitor, the tunablecapacitor coupled to an output of the receiver. Other implementations ofthis aspect include corresponding systems, circuitry, controllers,apparatus, and computer programs, configured to perform the actions ofthe methods, encoded on computer storage devices.

In a sixth general aspect, the disclosure features a method forprotecting a wireless power system during a load short condition inwhich a load is shorted at an output of a rectifier of a wireless powerreceiver, the wireless power system comprising the wireless powerreceiver and a wireless power transmitter, the wireless power receiverconfigured to receive power from the wireless power transmitter. Themethod includes detecting, by a voltage sensor coupled to the rectifieroutput, an undervoltage condition. Shorting, by a first controller, afirst protection switch coupled to a tunable capacitor of the wirelesspower receiver. Detecting, by a current sensor coupled a tunablecapacitor of the wireless power transmitter, an overcurrent condition inthe tunable capacitor. Shorting, by a second controller, a secondprotection switch coupled to a tunable capacitor of the wireless powertransmitter. Other implementations of this aspect include correspondingsystems, circuitry, controllers, apparatus, and computer programs,configured to perform the actions of the methods, encoded on computerstorage devices. In some implementations, the method includes shuttingoff an inverter of the wireless power transmitter, the inverter coupledto the tunable capacitor of the wireless power transmitter.

In a seventh general aspect, the disclosure features a method forprotecting a bidirectional wireless power system during a loaddisconnect condition in which the load is disconnected from an output ofa ground side inverter of a ground side wireless power transmitter, thebidirectional wireless power system comprising the wireless powertransmitter and a wireless power receiver, and the wireless powertransmitter configured to receive power from the bidirectional wirelesspower receiver. The method includes detecting, by a load disconnectsensor, a load disconnect condition. Shutting off, by a firstcontroller, the ground-side inverter. Shorting, by a second controller,a first TMN-protection switch coupled to a first ground-side tunablecapacitor, the at least one tunable capacitor coupled to an input of theground-side inverter. Switching in, by the first controller, a firstresistor parallel with the disconnected load. Transmitting an errorsignal from the wireless power transmitter to the wireless powerreceiver. Upon receipt of the error signal, shutting off, by a thirdcontroller, the vehicle-side inverter. Other implementations of thisaspect include corresponding systems, circuitry, controllers, apparatus,and computer programs, configured to perform the actions of the methods,encoded on computer storage devices.

Particular implementations of the subject matter described in thisspecification can be implemented so as to realize one or more of thefollowing advantages. Implementations may provide a modular sensornetwork that can be readily configured for use on either a wirelesspower transmitter or receiver. Implementations may provide a modularsensor network that can be readily configured for use on either awireless power transmitter or receiver. Implementations may provide asensor/protection network that can be used with either uni-directionalor bidirectional wireless power transfer systems. Implementationsprovide a sensor network capable of making remote measurements ofresonator coil current. For example, implementation can provide so thesensor network is capable of measuring the current through a transmitterresonator coil that is positioned remote (e.g., along a 8-10 foot cable)from the sensors and other control circuitry of the wireless powertransmitter. In some implementations that use analog circuitry toimplement sensors and protection circuitry may provide faster protectionresponse to hazardous operating conditions. Some implementations provideprotection without reliance on communication schemes. For example,implementations can initiate protective actions between a wireless powerreceiver and a wireless power transmitter without reliance on a wired orwireless communication link in a forward and reverse charging direction.Some implementations allow for modularity of non-redundant hardware,code, and memory. For example, assigning operating personalities tocomponents in bidirectional systems can allow for greater modularity ofhardware and software, which may allow for fast, safe, and on-the-flyfor power reversals. In addition, the increased modularity may increaseefficiency in product manufacturing.

Implementations of the devices, circuits, and systems disclosed can alsoinclude any of the other features disclosed herein, including featuresdisclosed in combination with different implementations, and in anycombination as appropriate.

The details of one or more implementations of the subject matterdescribed in this specification are set forth in the accompanyingdrawings and the description below. Other features, aspects, andadvantages of the subject matter will be apparent from the description,the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a schematic model of an exemplary wireless powertransmitter.

FIG. 1B is a diagram of a schematic model of an exemplary wireless powerreceiver.

FIG. 1C is a block diagram of an exemplary sensor network for use inwireless power systems.

FIG. 1D is a block diagram of an exemplary protection network for use inwireless power transfer systems.

FIG. 2A is a schematic of an exemplary voltage sensor for the tunablematching networks (TMNs).

FIG. 2B is a plot showing an exemplary waveform output of the voltagesensor as compared to a waveform output of a direct voltage measurementat the tunable capacitor.

FIGS. 3A-3C are schematics of an exemplary voltage sensor across one ormore capacitors in position C2 of the wireless power transmitter orreceiver.

FIG. 3D is a plot of an exemplary waveform output of voltage sensor andexemplary waveform output of a direct measurement of V_(C2) voltage(VC2+, VC2−) provided in FIGS. 1A-1B.

FIGS. 3E-3F are plots of exemplary waveforms of voltages VC2_diff, Vy,and VC2_sense.

FIG. 4A is a schematic of an exemplary current sensor to compute currentI1 at inductor Ls1.

FIG. 4B is a plot of an exemplary waveform output of current sensor andexemplary waveform output of a direct measurement of the current I1 atinductor Ls1.

FIG. 4C is a plot of an exemplary waveform of voltage Vc2_diff.

FIG. 4D is a plot of an exemplary waveform of voltage V1.

FIG. 5A is a schematic of an exemplary current phase detect circuithaving inputs CS1 and CS2 from a current sense transformer (CST).

FIG. 5B is a schematic of an exemplary circuit configured to generate areset signal for the peak detect circuits.

FIG. 5C is an exemplary peak detector circuit configured to detect thepeak(s) of voltage signal VC2_sense.

FIG. 5D is an exemplary peak detect circuit configured to detect thepeak(s) of the signal representing coil current V_I1_sense.

FIG. 5E is a plot of an exemplary waveform output of the circuit in FIG.5A.

FIG. 5F is a plot of an exemplary waveform of input voltage signalVC2_sense and an exemplary waveform of output VC2_peak_detect.

FIG. 5G is a plot of an exemplary waveform of input signal V_I1_senseand an exemplary waveform of output V_I1_sense_pk.

FIG. 5H is a plot of an exemplary waveform output of the reset voltagesignal Vreset.

FIG. 6A is an exemplary peak detector circuit configured to sample thecurrent in the TMN of the transmitter or receiver.

FIG. 6B is an exemplary zero-crossing detector circuit.

FIGS. 7A-7E are schematics of exemplary window comparator circuitsconfigured to detect overvoltage or undervoltage conditions for signalswithin the system.

FIGS. 8A-8E are schematics of exemplary fault latch circuits configuredto latch when a fault is detected.

FIG. 8F is a schematic of an exemplary latch circuit that combines twoor more of the faults from the latch circuits in FIGS. 8A-8E.

FIGS. 9A and 9B are schematics of an exemplary protection circuit for aTNN.

FIG. 10A illustrates the effect of a latched fault in an exemplarytransmitter at time when the duty cycle is great than zero.

FIG. 10B illustrates the effect of a latched fault when the duty cycleequals zero.

FIG. 11A is a digital logic circuit to enable or disable switching inthe TMN if there is a hardware fault (HW_FAULT) or external fault(EXT_FAULT).

FIG. 11B is a switch to enable or disable the hardware protection.

FIG. 12 is an exemplary plot of waveforms during a hardware test of aTMN overvoltage fault condition.

FIG. 13 is an exemplary wireless power system having one or moreprotection mechanisms.

FIG. 14 is a plot of exemplary waveforms in exemplary wireless powersystem during a load disconnect condition.

FIG. 15 is a plot of exemplary waveforms in exemplary wireless powersystem during a load short condition.

FIG. 16 is a schematic of an exemplary bidirectional wireless powertransfer system.

FIG. 17 depicts flowchart of an exemplary bidirectional control processthat can be executed in accordance with implementations of the presentdisclosure.

FIG. 18 depicts a schematic of an exemplary inverter-rectifier and atiming diagram illustrating operation of the inverter-rectifier in aninverter operating mode.

FIG. 19 depicts a schematic of an exemplary inverter-rectifier and atiming diagram illustrating operation of the inverter-rectifier in arectifier operating mode.

FIG. 20 depicts a flowchart of exemplary protection operations that canbe executed in accordance with implementations of the present disclosure

FIG. 21 is a diagram of a bidirectional wireless power transfer devicethat illustrates an arrangement of fault sensing circuits.

FIG. 22A is a block diagram of exemplary protection logic for abidirectional wireless power transfer device.

FIG. 22B illustrates logic truth tables associated with the exemplaryprotection logic shown in FIG. 22A.

FIG. 23 shows a series of diagrams depicting the operation of theinverter-rectifier in response to a load disconnect when assigned arectifier operating personality.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

In general, the disclosure features control and protection systems foruni-directional and bidirectional wireless power transfer systems.Implementations include sensor and protection networks to protectwireless power transfer systems from various hazardous conditionsincluding overvoltage, overcurrent, over-temperature, and sudden changesto power that may cause damage to the system. Implementations includecontrol systems for managing the shutdown of wireless power transmissionsystem components (e.g., tunable matching networks, inverters,rectifiers, and inverter-rectifiers) in response to a protective action.Implementations include control systems and processes for managing thereversal of power flow in a bidirectional wireless power transfersystem.

FIG. 1A is a diagram of an equivalent model of an exemplary wirelesspower transmitter 100 (also known as a wireless power source or groundassembly (GA)). The wireless power transmitter 100 is part of an overallwireless power system that further includes a wireless power receiver112 (in FIG. 1B) that is configured to receive power transmitted by thewireless power transmitter 100. A wireless power transmitter 100 isgenerally coupled to a power supply such as a power grid, AC generator,etc. Furthermore, the wireless power transmitter 100 is generally usedto transfer power from the power supply to power a load or charge abattery coupled to a wireless power receiver 112. This mode of operationis referred to herein as the normal operating mode and is used inreference to the normal power flow direction in a uni-directionalwireless power transfer system. However, power flow can be reversed(e.g. a reverse power flow direction) in a bidirectional wireless powertransfer system. Such operation would be considered a reverse operatingmode. For example, in a bidirectional wireless power transfer system thetransmitter 100 can operate as a “receiver” and the receiver 112 canoperate as a “transmitter,” for example, to transfer power from battery,or a stored power source, to a load coupled to the transmitter 100. Forexample, during a power outage, a battery of an electric vehicle couldbe used to provide emergency power to a home through a bidirectionalwireless power system. Accordingly, the terms “transmitter” and“receiver” as used herein are in reference to respective components isin reference to their function in the normal operating mode, but is notintended to limit their function to either transmitter or receivingpower alone.

The exemplary wireless power transmitter 100 includes an inverter 102,which receives an input voltage and is coupled to an impedance matchingnetwork 103 and a resonator coil 104. Note that the model takes intoaccount the equivalent reflected impedance R_(ref1) 105 of the wirelesspower receiver and load that is reflected to the transmitter. Within theimpedance matching network 103 is a tunable matching network (TMN) 106having at least one first tunable capacitor. In this example, the TMN106 includes a first tunable capacitor 108 a and a second tunablecapacitor 108 b. In some implementations, the TMN 106 is coupled to oneor more controllers 109, such as a microcontroller, configured toprovide control signals such as tuning signals to tune the tunablecapacitors 108 a-108 b, protection signals to protect the TMN 106 fromdamage, and the like. Examples and description of tunable matchingnetworks can be found in commonly owned U.S. patent application Ser. No.15/427,186 filed on Feb. 8, 2017 and titled “PWM capacitor control”.

In the exemplary implementation shown in FIG. 1A, the inverter 102provides a voltage (V1+, V1−) to the impedance matching circuit 103having inductors Ls3 a and Ls3 b. These inductors Ls3 a and Ls3 b arecoupled in series with a tunable capacitor 108 a and 108 b,respectively. Tunable capacitor 108 a has a first end with positivevoltage Vcap+ and a second end with negative voltage Vcap−. Tunablecapacitor 108 b has a first end with positive voltage Vcap++ and asecond end with negative voltage Vcap−−. Tunable capacitor 108 a iscoupled in series with an optional current sense transformer 110. Insome implementations, the tunable capacitors 108 a, 108 b can be coupledin series to fixed capacitors Cs3 a, Cs3 b respectively. Coupled to theright-hand ends of capacitors Cs3 a, Cs3 b is capacitor Cs2 havingvoltage (Vc2+, Vc2−). Coupled in parallel to capacitor Cs2 is capacitorCs1 a, inductor Ls1, and capacitor Cs1 b. Inductor Ls1, when driven, isconfigured to generate an oscillating magnetic field to transfer energyto a wireless power receiver. Note that any of the electrical componentsdiscussed herein may represent one or more components coupled to eachother. For example, a single capacitor in transmitter model 100 mayrepresent two or more capacitors coupled in parallel or in series. Notealso that any values of components indicated in any of the providedfigures are exemplary values and can be adjusted for specificapplications.

FIG. 1B is a diagram of an equivalent model of an exemplary wirelesspower receiver (also known as a wireless power device or vehicleassembly (VA)). The structure of the wireless power receiver largelymirrors the structure of the transmitter 100 with some importantdifferences. In the receiver model 112, a voltage is induced in thereceiver coil 114 when the transmitter 100 generates an oscillatingmagnetic field. The voltage source 116 in the receiver 112 models thisinduced voltage. The receiver coil 114 is coupled to a capacitornetwork, which includes capacitors C12 and C32 in series and capacitorC11 in parallel. Coupled in series to this network is a tunable matchingnetwork (TMN) 122 that includes a current sense transformer (CST) 118and tunable capacitors 120 a, 120 b. Note that the CST 118 and/ortunable capacitors 120 a, 120 b may be packaged together in a module,such as an integrated circuit (IC). Ultimately, the matched voltageoriginating from the receiver coil is rectified at rectifier 124 andoutputted to a load 126. In some implementations, the load 126 may be abattery manager coupled to a battery. In some implementations, the load126 may be the battery itself. In an exemplary implementation, asmoothing capacitor 128 may couple the output of the rectifier 124 tothe load 126 and serve to filter the rectified output. In someimplementations, the TMN 122 is coupled to one or more controllers 130,such as a microcontroller, configured to provide control signals such astuning signals to tune the tunable capacitors 120 a-120 b, protectionsignals to protect the TMN 122 from damage, and the like.

Note that many of the below implementations of sensors and protectionmechanisms are discussed in the context of the wireless powertransmitter. However, they can be applied to similar structures andfunctions of the wireless power receiver.

In some implementations, inverter 102 can be implemented as abidirectional inverter-rectifier as discussed in more detail below.Similarly, in some implementations, rectifier 124 can be implemented asa bidirectional inverter-rectifier as discussed in more detail below.

FIG. 1C is a block diagram of an example sensor network 132 for use inwireless power systems. For clarity, sensor network 132 is depicted inFIG. 1C as being implemented within a wireless power transmitter 100. Itshould be noted that, wireless power transmitter 100 is similar to thewireless power transmitter 100 illustrated in FIG. 1A, except that thewireless power transmitter 100 is represented as a block diagram ratherthan a schematic model. In addition, sensor network 132 can beimplemented within a wireless power receiver (e.g., wireless powerreceiver 112 shown in FIG. 1 ). For example, sensor network 132 can bearranged in a similar fashion within a wireless power receiver 112 tomeasure voltages and currents of wireless power receiver components thatcorrespond to the wireless power transmitter components discussed below.

Sensor network 132 includes TMN voltage sensors 134, differentialvoltage sensor 136, voltage sensor 138, current sensor 140, currentphase sensor 142, and current sensor 150. Each of sensors 134, 136, 138,140, 142, and 150 can be implemented as analog circuits as shown, forexample, in FIGS. 2A, 3A-3C, 4A, 5A, and 6A and described in more detailbelow. In some implementations, one or more of sensors 134, 136, 138,140, 142, and 150, or portions thereof, can be implemented in software.For example, voltages or currents measured by sensors 134, 136, 138,140, 142, and 150 can be converted from analog to digital and furtherprocessed by a microprocessor or microcontroller according to softwareinstructions.

TMN voltage sensors 134 are arranged to measure the voltage across TMN106. For example, TMN voltage sensor A is electrically connected oneither side of TMN A to measure the voltage drop across TMN A. Forexample, voltage sensor 134 is connected at Vcap+ and Vcap−. In someimplementations, the sensor network 132 can include one voltage sensor134 for each TMN 106 in a wireless power transmitter 100. For example, awireless power transmitter 100 may have only one TMN 106 and only onecorresponding voltage sensor 134, while in another implementation awireless power transmitter 100 may have multiple TMNs 106 with acorresponding voltage sensor 134 for each TMN 106. As described in moredetail below in reference to FIG. 2A, Voltage sensor 134 is configuredto generate an output voltage signal that represents the measuredvoltage across a TMN 106. In some examples, the output voltage signal isa single ended voltage signal, for example, a voltage signal that rangesbetween zero and a positive or negative bound (e.g., 0 to 3V or 0 to−3V).

Although illustrated as being in series with the resonator coil 104, insome implementations the TMN 106 is be arranged in parallel with theresonator coil 104. In such implementations, voltage sensor 134 can alsobe arranged in parallel with the TMN 106.

Differential voltage sensor 136 is arranged to measure the rate ofchange (e.g., the first derivative) of the voltage difference betweenportions of the impedance matching network. For example, differentialvoltage sensor 136 is arranged to measure the rate of change of thevoltage difference between the respective output terminals of TMN A andTMN B. For example, the differential voltage sensor 136 can be connectedat Vcap− and Vcap++. As described in more detail below in reference toFIGS. 3A and 3B, differential voltage sensor 136 is configured togenerate an output signal that represents the measured rate of change ofthe voltage between the outputs of TMNs 106. In some examples, theoutput voltage signal is a single ended voltage signal. The output ofthe differential voltage sensor 136 also represents the rate of changeof the voltage across capacitor C2 s. Two different transmitter 100parameters can be determined based on the differential voltage obtainedat this location in the transmitter 100; the voltage across capacitor C2s and the current through the resonator coil 104 (current I1 s).

Voltage sensor 138 is configured to measure the voltage across capacitorC2 s. As described in more detail below in reference to FIG. 3C, voltagesensor 136 is configured to generate an output signal that representsvoltage across capacitor C2 s. For example, voltage sensor 138 can beconfigured to integrate the output of differential voltage sensor 138 toprovide an output signal that represents the voltage across capacitor C2s, or more generally any parallel components of matching network. Insome examples, the output signal is a single ended voltage signal.

Current sensor 140 is configured to measure the current through theresonator coil 104 (e.g., current I1 s). As described in more detailbelow in reference to FIG. 4A, current sensor 140 is configured togenerate an output signal that represents current through the resonatorcoil 104. For example, current sensor 140 is configured to calculate thecurrent I2 s through capacitor C2 s based on the differential voltagemeasured by differential voltage sensor 136 and obtain the currentthrough the coil 104 by subtracting the calculated current I2 s from thecurrent I3 s through the impedance matching network as measured bycurrent sensor 150. In some examples, the output signal of currentsensor 140 is a single ended voltage signal.

Current sensor 150 is coupled to transformer 110, e.g., in a transmitter100. Similarly, currents sensor 150 can be coupled to a correspondingtransformer, e.g., CST 118 in a receiver 112. Current sensor 150 isconfigured to measure the current through the impedance matching network(e.g., current I3 s). As described in more detail below in reference toFIG. 6A, current sensor 150 is configured to generate an output signal(CSI) that represents current I3 s through the impedance matchingnetwork (e.g., TMN 106, inductor L3 sA, and capacitor C3 sA).

Current phase sensor 142 is configured to measure the phase of thecurrent I3 s through the impedance matching network. As described inmore detail below in reference to FIG. 5A, current phase sensor 142 isconfigured to generate an output signal that represents phase of currentI3 s.

In some implementation of a wireless power transmitter 100 it is notpractical to directly measure the current through the resonator coil 104because the coil may be located at the end of a cable that is at adistance from the transmitter's control circuitry. In such situations,the indirect measurements provided by the sensor network 132 may provideaccurate and efficient current measurements to effectively maintain safeoperations of the wireless power transmitter 100. In someimplementations, the sensors in sensor network 132 can be implemented inanalog circuitry. Such implementations may provide faster detection andresponse to hazardous conditions than digital circuitry or softwarebased sensors.

In some implementations, differential voltage sensor 136 is configuredto scale its output signal based the current measurement obtained bycurrent sensor 150. For example, the differential voltage sensor 136 canscale its output signal to account for a voltage drop across capacitorsC3 sA and C3 sB (when present in a transmitter 100) based on the output(CSI) of current sensor 150.

FIG. 1D is a block diagram of an exemplary protection network 180 foruse in wireless power transfer systems. Protection network 180incorporates sensor network 132. Protection network 180 is configured togenerate faults in response to detecting a hazardous operating conditionin the wireless power transmitter 100 (or receiver 112). Protectionnetwork 180 can also be configured to perform protective actions for awireless power transmitter 100 (or receiver 112) in response todetecting a hazardous operating condition. Hazardous operatingconditions can include, but are not limited to, over/undervoltage/current conditions in the impedance matching network and/or TMN,over/under voltage/current conditions at the resonator coil, over/undervoltage conditions at capacitor C2. These or other hazardous operationconditions can be indicative of one or more operational faults withinthe wireless power transfer system including, but not limited to, a loadshort, a load disconnect, the presence of foreign object debris (FOD)too close to the resonator coil 104, or a failure of one or morecomponents of the transmitter 100 or receiver 112.

Protection network 180 includes sensor network 132, peak detectors 146,148, 151, reset signal generator 144, comparator circuits 152-160, faultlogic 162-170, optional combined fault logic 172, and protection/controlcircuitry 109. Each of the components of protection network 180 can beimplemented as analog circuits as shown, for example, in FIGS. 2A,3A-3C, 4A, 5A, 6A, 6B, 7A-7E, and 8A-8F and described in more detailbelow. In some implementations, one or more of sensors 134, 136, 138,140, 142, and 150, or portions thereof, can be implemented can beimplemented in software. For example, voltages or currents measured bysensors 134, 136, 138, 140, 142, and 150 can be converted from analog todigital and further processed by a microprocessor or microcontrolleraccording to software instructions.

Protection/control circuitry can include separate protection and controlcircuitry for the TMN (e.g., TMN protection/control circuitry 174) andfor the inverter (or rectifier in a receiver) (e.g., inverterprotection/control circuitry 176). Furthermore, the protection andcontrol functions of the protection/control circuitry 109 can beintegrated (e.g., into a signal a common processor or set of processors)or segmented (e.g., in which separate protection circuitry functionsseparately to override normal control signals from control circuitryduring in response to a fault condition). The protection/controlcircuitry 109 can be implemented in hardware, software, or a combinationthereof. For example, the protection/control circuitry 109 can beimplemented as one or more software programs executed by one or moreprocessors. The protection/control circuitry 109 can be implemented inanalog or digital circuits. For example, the protection/controlcircuitry 109 can be implemented as analog circuitry, as an ASIC, or asan FPGA.

The current phase sensor 142, and the peak detectors 146, 148, 151,provide output signals to the TMN protection/control circuitry 174 whichcan be used to control the operations of the TMN 106. The details of thecurrent phase sensor 142 and the peak detectors 146, 148, and 151 aredescribed below in reference to FIGS. 5A, 5D, 5C, and 6A. Generally,peak detector 146 generates an output signal that indicates the timing,magnitude, or both of voltage peaks (e.g., positive and negative peaks)across capacitor C2 s based on the output of voltage sensor 138. Peakdetector 148 generates an output signal that indicates the timing,magnitude, or both of current peaks (e.g., positive and negative peaks)through the resonator coil 104 based on the output of current sensor140. Peak detector 151 generates an output signal that indicates thetiming, magnitude, or both of current peaks (e.g., positive and negativepeaks) through the impedance matching network (e.g., 13 s) based on theoutput of current sensor 150. Reset signal generator 144 generates areset signal that is used to reset the circuitry in peak detectors 148and 146. Reset signal generator 144 is configured to generate the resetsignal based on the output of differential voltage sensor 136.

The comparator circuits 152-160 and fault logic 162-170 detect abnormaloutput values from respective sensors in sensor network 132 and generatecorresponding fault signals. The details of the comparator circuits152-160 and fault logic 162-170 are described below in reference toFIGS. 7A-7E and 8A-8E. Generally, the comparator circuits 152-160 detectabnormal conditions in the transmitter 100 by comparing an output of arespective sensor to one or more threshold values. The fault logic162-170 receives an output from a respective one of the comparatorcircuits 152-160 and generates a fault detection signal if an abnormalcondition is detected. For example, the fault logic 162-170 can includea latch circuit that latches (e.g., temporarily or permanently stores)the output of a comparator circuit when a fault is indicated. Inresponse, the fault logic passes a fault signal to either the combinedfault logic 172 (if available) or to one or both of the TMN and inverterprotection/control circuitry 174, 176. If the combined fault logic 172is not implemented, each fault logic 162-170 passes its output alongsignal paths 178 to the protection/control circuitry 109.

TMN protection/control circuitry 174 is configured to shutdown or bypassthe TMN 106 (or TMNs 106) in response to the detection of a fault in thewireless power transmission system. As described in more detail below inreference to FIGS. 9A-10B, TMN protection/control circuitry 174 isconfigured to bypass the TMN in response to a fault. For example, theTMN protection/control circuitry 174 can be configured to bypass the TMN106 by routing current around the TMN (e.g., shorting the TMN). In someimplementations, TMN protection/control circuitry 174 is configured tobypass the TMN 106 by retaining (e.g., latching) one or more controlsignals (such as a pulse width modulation (PWM) signal) in an assertedstate. An asserted state refers to a signal value that holds a bypasstransistor in an “on” state. For example, an asserted state for a P-typetransistor may be a negative drive signal whereas an asserted state foran N-type transistor may be a positive drive signal. In someimplementations, TMN protection/control circuitry 174 can delay latchingthe control signal until the voltage across the TMN is below a thresholdvalue (e.g., 50 V), for example, to minimize current transients.

Inverter (or rectifier) protection/control circuitry 176 is configuredto shutdown the inverter 102 (or rectifier 124) in response to thedetection of a fault in the wireless power transmission system. Asdescribed in more detail below in reference to FIGS. 14 , and 20-23,inverter protection/control circuitry 176 is configured to shutdown theinverter in response to a fault by isolating the inverter (rectifier)from a power source to stop current flow through the transmitter 100(receiver 112).

FIG. 2A is a schematic of an exemplary voltage sensor 134 for thetunable matching networks (TMNs) 106 and 122. An instance of the voltagesensor 134 can be coupled to each of the tunable capacitors 108 a, 108 bof the TMN 106 or to each of the tunable capacitors 120 a, 120 b of theTMN 122. For example, in TMN 106, lead 202 a of a first instance ofvoltage sensor 134 is configured to be coupled to voltage node Vcap+ oftunable capacitor 108 a and lead 202 b of the first instance of voltagesensor 134 is configured to be coupled to voltage node Vcap− of tunablecapacitor 108 a. Similarly, lead 202 a of a second instance of voltagesensor 134 is configured to be coupled to voltage node Vcap++ of tunablecapacitor 108 b and lead 202 b of the second instance of voltage sensor134 is configured to be coupled to voltage node Vcap−− of tunablecapacitor 108 b. Thus, in an exemplary tunable matching network havingtwo tunable capacitors, there are two voltage sensors, each coupled to atunable capacitor.

The exemplary voltage sensor 134 is a two-stage sensor having a first orpassive stage 204 and a second or amplification stage 206. The exemplarypassive stage 204 includes a capacitive coupler (made up of capacitorsC17 and C18) that couples the voltage at leads 202 a, 202 b to the restof the sensor circuit. In some implementations, the passive stage 204may include a capacitive coupler, resistive divider, magnetic coupler,optical coupler, or any combination of these. Coupled to the capacitivecoupler is a capacitive divider made up of capacitors C20 and C21. Thecapacitor divider divides the voltage coupled into the sensor forpassing to the amplification stage 206. The capacitor divider includes abias voltage 207. The bias voltage can be set in a range between 0 and 2volts, or, in some implementations between 1 and 1.5 volts. Theamplification stage 206 is a unity gain amplifier U13 that converts thedifferential voltage from the passive stage 204 to a single-endedvoltage output Vcap_sense2. Note the bias voltage 208 on the positiveinput to the amplifier U13. The bias voltage 208 may be, for this sensorconfiguration, between 0 V and 3 V. In other implementations, the biasvoltage 208 is tailored for the specific sensor configuration and canhave a different value. In some implementations, the amplifier may beimplemented using a single positive or dual voltage power supply.Although a capacitive divider is shown in the figure as part of thevoltage sensor, a resistive divider may be used as the voltage sensor.In some implementations, the unity gain amplifier serves as a filter.For example, the amplification stage 206 can be configured as a low passfilter (e.g., with a bandwidth of approximately 0-2 MHz).

FIG. 2B is a plot showing an exemplary waveform 210 of the output ofvoltage sensor 134 as compared to a waveform 212 of a direct voltagemeasurement at the tunable capacitor 108 a or 108 b. The two waveforms,210 and 212, overlay one another. Due to the high degree of accuracy,the difference between the sensor waveform 210 (light waveform) isnearly imperceptible from the waveform 212 (dark waveform) of the directmeasurement. In some implementations, the accuracy of the voltage sensorcan be within +/−10%, +/−5%, or less of the direct voltage measurement.To produce waveform 210, the bias voltage is subtracted from thesingle-ended voltage output Vcap_sense2 and the difference is scaled bythe sensor gain. Thus, the waveform 210 is defined by the followingrelationship: waveform 210=(Vcap_sense2−bias voltage 208)*sensor gain.In the plot shown in FIG. 2B, the bias voltage 208 is 1.5 V which can bemodified for the needs of a specific wireless power transmitter orreceiver. In the plot an artificial sensor gain of 750 is applied toshow correspondence of the sensor waveform 210 and the measured voltagewaveform 212.

In some implementations, the output Vcap_sense2 of the voltage sensor ispassed to one or more protection mechanisms. For example, the outputVcap_sense2 can be passed to a window comparator to determine theexistence of an overvoltage condition in TMN 106 or 122. For example, ifa desirable voltage level for this particular system is 500-550 V, thenan error signal may be produced if the output of the sensor reads over550 V. This error signal can be used to prevent any potential damage dueto an overvoltage condition in TMN 106 or 122. In anotherimplementation, the output Vcap_sense2 is passed to a controller 109coupled to TMN 106 or 122. The controller 109 can digitize the outputVcap_sense2 for use in controlling the tunable capacitor(s) within TMN106 or 122. In yet another implementation, the output Vcap_sense2 of thevoltage sensor is passed to both protection mechanism(s) and tocontroller(s).

FIG. 3A is a schematic of an exemplary first stage 300 of a differentialvoltage sensor 136 across one or more capacitors in position C2 of thewireless power transmitter (capacitor Cs2) or receiver (capacitor Cd2).The operational amplifier U5 in the first stage 300 of the differentialvoltage sensor 136 acts as a differentiator. The output of the firststage 300 is a single-ended voltage Vy that is passed to the secondstage 302 in FIG. 3B. The second stage 302 includes an amplifier U10that is a unity gain amplifier with inputs Vy and 304. For a voltagesensor implemented in a transmitter, input 304 is equal to the biasvoltage if the impedance matching network 103 of transmitter 100 doesnot include the fixed capacitors Cs3 a, Cs3 b. If, however, network 103includes the fixed capacitors Cs3 a, Cs3 b, then V1 is used for input304. V1 is the TMN input current information. The output of the secondstage 302 is the differential voltage at position C2, VC2_diff. Theimplementation in the receiver mirrors that of the transmitter.

FIG. 3C is a schematic of voltage sensor 138 which includes an amplifierU7 in an integrator configuration. The differential voltage Vc2_diff ispassed to the negative input of the amplifier U7 with a bias voltage atthe positive input. The output of the third stage 306 is voltage signalVC2_sense.

FIG. 3D is a plot of an exemplary waveform output 310 of voltage sensor138 and exemplary waveform output 312 of a direct measurement of V_(C2)voltage (VC2+, VC2−) (provided in FIGS. 1A-1B). The waveform output 310is attained by the following relationship: output310=−((VC2_sense2)−bias voltage)*sensor gain, where the bias voltageequals 1.5 V and sensor gain is 1000. Note that phase of VC2_sense isnegative (see a plot of the original VC2_sense waveform in FIG. 3F).FIG. 3E is a plot of exemplary waveforms of voltages VC2_diff and Vy.Note that these waveforms were produced with fixed capacitors Cs3 a=Cs3b=300 nF.

FIG. 4A is a schematic of an exemplary current sensor 140 to computecurrent I1 in the transmitter 100. The differentiator circuit 400 usesmeasurements VC2_diff, which contains current information throughcapacitor Cs2 or C2 d (see waveform in FIG. 4C), and V1, which is thecurrent information through portion 111 of the impedance matchingnetwork 103 (see waveform in FIG. 4D) to output the differential signal,V_I1_sense, which has coil current information. The differential currentsignal is attained by subtracting the current through capacitor Cs2 fromthe current from the TMN 106.

FIG. 4B is a plot of an exemplary waveform output 402 of current sensor140 and exemplary waveform output 404 of a direct measurement of thecurrent I1 in the transmitter 100. The waveform output 402 is attainedby the following relationship: output 402=((V_I1_sense)−biasvoltage)*sensor gain, where the bias voltage equals 1.5 V and sensorgain is 142.5. Note that it is difficult to perceive the differencebetween the waveforms of current sensor 140 output and the directmeasurement I(Ls1) due to the high accuracy of current sensor 140. FIG.4C is a plot of an exemplary waveform of voltage Vc2_diff and FIG. 4D isa plot of an exemplary waveform of voltage V1.

FIG. 5A is a schematic of an exemplary current phase detector 142 havinginputs CS1 and CS2 from CST 110 or 118. In some implementations, thesensor 142 is configured to detect the phase of the current signal (I3current) from tunable capacitor 108 a or tunable capacitor 120 a. Insome implementations, sensor 142 is configured to detect rising orfalling current phase (CP) or both. FIG. 5E is a plot of an exemplarywaveform output 502 (in dashed line) of sensor 142. The waveform 502 isa square wave representing output CP of sensor 142. In animplementation, an analog-to-digital converter of the controller sampleson the positive transition (of a rising edge) and/or negative transition(of a falling edge) of waveform 502. The current phase sensor caninclude filters to filter out harmonics. The filters can be after thecurrent sense transformer. For example, the filter can include a lowpass filter, a high pass filter, a bandpass filter, and/or a band-stopfilter.

FIG. 5B is a schematic of an exemplary reset generator 144 configured togenerate a reset signal for the peak detect circuits 506, 508. Theinputs of reset generator 144 are differential voltage signal VC2_diffand bias voltage (1.5 V in this example). The circuit 144 outputs avoltage reset signal Vreset. FIG. 5H is a plot of an exemplary waveformoutput 510 of the reset voltage signal Vreset. The reset signal Vreset510 is generated once a cycle of differential voltage signal VC2_diffand placed on the rising edge of the voltage signal VC2_sense.

FIG. 5C is an exemplary peak detector 146 configured to detect thepeak(s) of voltage signal VC2_sense. Thus, circuit 146 uses voltagesignals VC2_sense and Vreset to output peak detection signalVC2_peak_detect. FIG. 5F is a plot of an exemplary waveform of inputvoltage signal VC2_sense 512 and an exemplary waveform of outputVC2_peak_detect 514. Note that the peak detect signal 514 sustains thepeak of voltage signal VC2_sense 512 until the reset signal Vreset 510triggers.

FIG. 5D is an exemplary peak detector 148 configured to detect thepeak(s) of the signal representing coil current V_I1_sense. Thus,circuit 148 uses voltage signals V_I1_sense and Vreset to output peakdetection signal V_I1_sense_pk. FIG. 5G is a plot of an exemplarywaveform of input signal V_I1_sense 518 and an exemplary waveform ofoutput V_I1_sense_pk 520. Note that the peak detect signal 520 sustainsthe peak of voltage signal V_I1_sense 518 until the reset signal Vreset510 triggers.

FIG. 6A is a schematic of an exemplary current sensor 150 and peakdetector 151. Peak detector 151 is configured to sample the current inTMN 106 or 122. Note that, in an exemplary implementation, an integrator602 is included in the peak detector 151. This configuration has anadvantage over, for example, a differentiator, in that integrator 602can attenuate noise at frequencies above the operating frequency of thewireless power system. An exemplary operating frequency is 85 kHz. Toobtain information about the current in the TMN, the output CSI2 of theintegrator 602 is sampled by the current phase signal 502. Thisimplementation avoids being affected by switching noise associated withthe inverter 102. FIG. 6B is an exemplary zero-crossing detector (ZCD)circuit 604. Zero crossing detector circuit outputs the digital CPsignal, which is high when the current in the TMN is negative and lowwhen the current is positive.

FIGS. 7A-7E show schematics of exemplary comparator circuits 152-160.Comparator circuits 152-160 are window comparator circuits configured todetect overvoltage or undervoltage conditions for signals within thesystem. In some implementations, the window comparator circuit can becoupled to the various measurement circuits described herein. Forexample, comparator circuits 156 or 158 can be coupled to the output ofthe voltage sensor 134 to detect an overvoltage condition of any oftunable capacitors 108 a, 108 b, 120 a, or 120 b. In someimplementations, the window comparator circuits each produce a count foreach time the input value is outside a preset window defined by an upperlimit and a lower limit. For example, the window comparator circuit 700produces a count signal nVtmnB_HIGH when the TMN voltage signal VtmnB isgreater than 550 V and count signal nVtmnB_LOW when the TMN voltagesignal VtmnB is less than −550 V. Each TMN voltage signals VtmnA, VtmnBare measured by voltage sensor 134. In other words, VtmnA equals outputsignal Vcap_sense2 for a voltage sensor 134 on tunable capacitor 108 a(transmitter) or 120 a (receiver). VtmnB equals output signalVcap_sense2 for a voltage sensor 134 on tunable capacitor 108 b(transmitter) or 120 b (receiver).

Note that an overcurrent or undercurrent condition can be derived fromthe detected overvoltage or undervoltage conditions. For example, FIG.7B is a window comparator circuit 154 with input voltage inputV_I1_sense that is converted into a current reading. The below tablelists the exemplary window comparator circuits shown in FIGS. 7A-7E andtheir respective inputs and outputs.

TABLE 1 Input and output signals for window comparators. Figure InputDesignation Signals Output Signals FIG. 7A VC2_sense nVC2_LOW, nVC2_HIGHFIG. 7B V_I1_sense nI1_LOW, nI1_HIGH FIG. 7C VtmnB nVtmnB_LOW,nVtmnB_HIGH FIG. 7D VtmnA nVtmnA_LOW, nVtmn_HIGH FIG. 7E CSI1 nCSI_LOW,nCSI_HIGH

FIGS. 8A-8E are schematics of exemplary fault logic circuits 162-170configured to latch when a fault is detected. The output signals fromthe window comparators 152-160 are fed into the logic circuits which areconfigured to latch or turn off a circuit in case of a value outside ofpredetermined thresholds. For example, the count signals nVtmnB_LOW,nVtmnB_HIGH from window comparator 156 are input into fault logic 166.The exemplary fault logic 166 includes a NAND gate 802 which provides anoutput to a flip-flop circuit 804, producing fault signal VtmnB_FAULT.

Below is a table of exemplary latch circuits and their respective inputsand outputs.

TABLE 2 Input and output signals for window comparators. FigureDesignation Input Signals Output Signals FIG. 8A nVC2_LOW, nVC2_HIGHVC2_FAULT FIG. 8B nI1_LOW, nI1_HIGH V_I1_FAULT FIG. 8C nVtmnB_LOW,VtmnB_FAULT nVtmnB_HIGH FIG. 8D nVtmnA_LOW, VtmnA_FAULT nVtmn_HIGH FIG.8E nCSI_LOW, nCSI_HIGH CSI1_FAULT

FIG. 8F is a schematic of an exemplary combined fault logic 172 andincludes logic circuit 808 that combines fault output signals from twoor more of the fault logic circuits in FIGS. 8A-8E. For example, asillustrated, the combined fault logic 172 combines fault output signalsfrom two or more of the fault logic circuits in FIGS. 8A-8E using logicOR gates. In some implementations, the controller 109 and/or 130 isconfigured to read each of the fault signals independently. In otherimplementations, the controller 109 and/or 130 is configured to read theoutput of the logic circuit 808, which produces an overall hardwarefault signal HW_FAULT. In some implementations, the controller can readany combination of the fault signals described herein.

FIG. 9A is an exemplary detection circuit configured to detect if theTMN voltage is low voltage while TMN duty cycle is zero. The detectioncircuit takes in PWM signals, s_PWM_1 and s_PWM_2, which are generatedby the controller 109 or 130 to control the switches (e.g., FETs) of theTMN 106 or 122, respectively, and outputs detection signal fet_low.These PWM signals and the detection signal fet_low is input to circuits902 and 904 (as shown in FIG. 9B) to produce the control signals,s_PWM_1_o and s_PWM_2_o, which are configured to control the switches ofthe TMN. Fault signal latch_fets short the switches of the TMN toprotect the switches from damage.

In a first implementation, when the duty cycle of a TMN is greater thanzero and a fault is detected, the TMN voltage is allowed to decrease tozero before the switches of the TMN are shorted. This prevents anydamage from occurring from the short. FIG. 10A illustrates the effect ofa latched fault in an exemplary transmitter at time 1000 when the dutycycle is great than zero. The signal V(latch_fets) goes to 1 V and thevoltage V(s_Vcap+, s_Vcap−) at tunable capacitor 108 a goes to zero.

In a second implementation, when the duty cycle of a TMN is zero and afault is detected, shut down occurs when the voltage in the TMN reachesa particular low range, such as within +/−50 V. FIG. 10B illustrates theeffect of a latched fault when the duty cycle=0. At time 1002, the latchsignal goes to 1 V. The voltage V(s_Vcap+, s_Vcap−) at the tunablecapacitor 108 a has some magnitude and is allowed to approach 50 Vbefore going to zero at time 1004. The FIG. 10B graph illustrates theoperation of the TMN protection/control circuitry 174 to delay latchingthe control signal until the voltage across the TMN is below a thresholdvalue (e.g., 50 V), for example, to minimize current transients.

FIG. 11A is a digital logic circuit to enable or disable switching in ofthe TMN if there is a hardware fault (HW_FAULT) or external fault(EXT_FAULT). FIG. 11B is a switch to enable or disable the hardwareprotection. Note that if pins 2 and 3 are switched on, the hardware isenabled to latch the TMN switches on. If pins 1 and 4 are switched on,the enable signal is bypassed. In some implementations, if a fault isdetected, the TMN is configured to be shut down within one switchingcycle of the TMN switches.

FIG. 12 is an exemplary plot of waveforms during a hardware test of aTMN overvoltage fault condition. Output voltage 1202 and output current1204 are from the exemplary inverter 102. Waveform 1206 represents thevoltage at the TMN while waveform 1208 represents the TMN overvoltagefault signal. At time 1210, a fault is detected as shown in waveform1208. A short time after, at time 1212, the inverter shuts down. At time1214, the switches of the TMN are forced short. This creates a bypass atthe TMN by routing current around the TMN. Note that when the voltage atthe TMN (e.g. at the tunable capacitor) is high, as it is in thisexample, the circuit waits for the voltage to decrease before shortingthe switches of the TMN.

FIG. 13 is an exemplary wireless power system 1302 having one or moreprotection mechanisms from various fault conditions. Exemplary faultconditions that can occur in system 1302 include, but are not limitedto: load disconnect (e.g., in which the load disconnects from thewireless power receiver); load short (e.g., in which the load isshorted); load overvoltage (e.g., in which a battery overcharges or aload disconnect occurs); coil overcurrent (e.g., in which overcurrentcondition is detected in resonator coil L1 d and/or L1 s); TMNovervoltage (e.g., in which an overvoltage condition occurs in TMN 122or 106); or a combination thereof. These fault conditions can causelarge transients in the system which can lead to the damage of variouscomponents. Note that one or more controllers coupled to one moresensors described herein may protect the system and the system'scomponents from damage. These controllers include controller 1304coupled to the inverter, controller 1306 coupled to the transmitter-sideTMN (Tx-TMN), controller 1308 coupled to the receiver-side TMIN(Tx-TMN), and controller 1310 coupled to the rectifier. In someimplementations, controller 1304 and 1306 may be one controller 1312. Insome implementations, controller 1308 and 1310 may be one controller1314. Described below are scenarios in which the sensors discussedherein mitigate these fault conditions.

FIG. 14 is a plot of exemplary waveforms in exemplary wireless powersystem 1302 during a load disconnect condition. At time 1402, the loaddisconnects due to various reasons. For example, a battery managercoupled to the battery may sense an unfavorable condition and disconnectthe battery from the wireless power receiver. The load disconnect causesthe charging current to go through the decoupling capacitor C7 at theoutput of the rectifier. Subsequently, voltage V(v_bus+) in the outputcapacitor C7 starts rising from time 1402 to time 1404. At time 1404, anovervoltage condition at the output capacitor C7 is detected. Anovervoltage fault signal (signal V(ov_flg)) may be generated. At or neartime 1404, protection switches S5, S6, S9, and S10 of FIG. 13 short therectifier 124. In some implementations, the rectifier 124 can be shortedby closing one set of switches, e.g., either the switches on the highside of the rectifier bridge S9 and S10 or the switches on the low sideof the rectifier bridge S5 and S6. This causes the voltage at the outputcapacitor C7 to stop rising. This may cause distorted current throughthe TMN 122; thus, at or near time 1404, protection switches short thereceiver-side TMN 122.

From time 1404 to 1406, the distorted reflected impedance in thetransmitter electronics causes the current in the inverter (currentsignal I(Ls3 a) at the output of the inverter) and resonator coil(current signal I(L1 s)) to rise. At time 1406, an overcurrent conditionat the inverter is detected and the inverter shuts off. At or near time1406, the switches of transmitter-side TMN 106 are shorted such that thecurrent through the TMN is diverted through the closed switches insteadof the capacitor. This prevents damage to the TMN. Note that many of thecurrent signals become distorted from time 1404 to time 1406. Thesesignals include the current at the output of the inverter I(Ls3 a), thecurrent in the transmitter resonator coil I(L1 s), the current in thereceiver resonator coil I(L1 d). These distortions can cause the varioussensors described herein to trigger. The overcurrent flag signalV(oc_flag) is generated when the peak of the current signal I(Ls3 a)goes above a threshold. After time 1406, the energy in the systemdecreases. In some implementations, the receiver may be able tocommunicate with the transmitter fast enough for the transmitter toprotect itself.

In some implementations, normally open voltage blocking switches can beprovided in parallel with the parallel capacitors C10 or C13 shown inFIG. 13 . For example, if the over current condition is detected at theinverter, the normally open switch in parallel with the capacitor C10can be closed, thus reducing any excess coil current in the coil L1 s.

In some implementations, a load disconnect may be initiated by thesystem itself. For example, a VA-side wireless power transfer system caninclude a sensor coupled to the controller. A value or range of valuesfrom the sensor may be read by the controller. For example, a collisionsensor (e.g. an accelerometer), may be coupled to the controller (1314,and/or 1310 on the vehicle side). A reading from the collision sensorsignifying another vehicle crashing into the charging vehicle can causethe load to disconnect. The controller can open at least one switch(e.g., relay, MOSFET, IGBT) coupled between an output of the rectifierand the load (on the positive and/or ground side) in response todetecting a fault value from the sensor. The system further protectsitself and the systems turns off and/or de-energizes via the response asshown in FIG. 14 .

In some implementations, instead of (or in addition to) detecting arising voltage on the output capacitor C7, a current sensor can becoupled to the output to the load. If the current sensor reads a zero(or approximately zero) current, then the system can detect a loaddisconnect condition.

FIG. 15 is a plot of exemplary waveforms in exemplary wireless powersystem 1302 during a load short condition. There are multiple reasons aload short condition may occur. For example, if the output capacitor C7fails, it can cause a short. If an output filter (such as forelectromagnetic interference (EMI) reduction purposes) fails, it cancause a short. If the rectifier fails, it too can cause a short. In theexample provided in FIG. 15 , a load short occurs at time 1502,illustrated by signal V(V_LOAD+). Shortly thereafter, at time 1504, theshort is detected. At this time, an undervoltage fault signal isgenerated (signal V(uv_flg)). To protect itself, the TMN switches alsoshort, as shown by voltage signal V(V2 d_1, d_Vcap−). After time 1504,an overcurrent condition is detected in the transmitter-side TMN 106and, subsequently, the switches of transmitter-side TMN 106 are shorted.At time 1506, an overcurrent condition is detected in the inverter (flagV(oc_flg)) and the inverter shuts off, causing the system tode-energize.

FIG. 16 shows schematic of an exemplary bidirectional wireless powersystem 1600. The schematic depicts both a ground assembly (GA) sidewireless power transfer device 1600 a and a device side wireless powertransfer device 1600 b. As noted above, the GA side wireless powertransfer device 1600 a generally operates as a wireless powertransmitter for the case of a similar uni-directional wireless powertransfer system. As discussed below, however, in the bidirectionalsystem the GA side refers generally to a wireless power transfer devicethat is coupled to or configured to be coupled to a stationary powersupply or load such as a power grid, AC generator, etc. Furthermore, theGA side system is generally capable of handling higher power, voltage,or current transients than the device side wireless power transferdevice 1600 b. On the other hand, the device side wireless powertransfer device 1600 b generally operates as a wireless power receiverfor the case of a similar uni-directional wireless power transfersystem. As discussed below, however, in the bidirectional system thedevice side refers generally to a wireless power transfer device that iscoupled to or configured to be coupled to a mobile (or generally morelimited) power supply or load such as a battery or a battery powereddevice (e.g., a computing device or an electric vehicle). The deviceside wireless power transfer device 1600 b can also be referred to as avehicle assembly (VA) or VA side device when used in the context of awireless power transfer device coupled to an electric vehicle or othermobile vehicle.

Both the GA wireless power transfer device 1600 a and the VA wirelesspower transfer device 1600 b include an inverter-rectifier 1602. Theinverter rectifier 1602 includes a bridge configuration of switchingelements. For example, the inverter-rectifier 1602 can include activeswitching elements, such as MOSFETs, which permit the inverter-rectifier1602 to operate as either an inverter or a rectifier in a bidirectionalsystem. As discussed in more detail below, the operating mode (alsoreferred to herein as an “operating personality) of theinverter-rectifier 1602 can be controlled based on the pattern of PWMcontrol signals supplied to the switching elements.

The system 1600 is able to power a load with power transfer in a firstdirection (e.g., a normal power flow direction), such as a battery of avehicle, off of power input to the ground side (GA). Alternatively, thesystem 1600 can supply power in a second direction (e.g., a reversepower flow direction), such as suppling power to a power grid coupled tothe GA side device 1600 a from a battery of an electric vehicle coupledto the VA side device 1600 b. As another example, the bidirectionalsystem 1600 can be used to power a home during a power outage from abattery of an electric vehicle battery parked in a garage. Note that anyor all of the sensors and protection mechanisms discussed above can beimplemented in the bidirectional system 1600 that uses theinverter-rectifier 1602. Where single components are shown, includingresistors, inductors, and capacitors, banks of components, including inseries and/or parallel can be utilized. Where tunable components areshown, fixed components can be included in series and/or parallel withthe tunable components. In some implementations, the controller 1304 and1306 can be combined in a single controller 1620. Likewise, in someimplementations, the controller 1308 and 1310 can be combined in asingle controller 1640. Furthermore controllers 1304, 1306, 1620, 1308,1310, and 1640 can be implemented in a configuration similar to controland protection circuitry 176 and 178 discussed above.

In some implementations, the controllers 1620 and 1640 include abidirectional manager. The bidirectional manager coordinates theconfiguration of different hardware and software components wirelesspower transfer device (e.g., either 1600 a/1600 b) according to thedirection of power flow as indicated by an operating personalityassigned to the device. For example, an operating personality of INVindicates that the inverter-rectifier is operating as an inverter andtherefore the wireless power transfer device 1600 a/1600 b is operatingas a transmitter. Similarly, for example, an operating personality ofREC indicates that the inverter-rectifier is operating as a rectifierand therefore the wireless power transfer device 1600 a/1600 b isoperating as a receiver. The bidirectional manager also coordinatestransitions from one direction of power flow to the opposite directionof power flow. For example, the bidirectional manager of the VA sidedevice 1600 b can communicate with the bidirectional manager of the GAside device 1600 a through a wireless communication link 1650 (e.g., aWiFi link) to coordinate a power reversal. The bidirectional manger canbe can be implemented as separate controller within each device 1600a/1600 b or in software.

More specifically, various hardware and software components of thesystem can have different operating setpoints, modes and/or ranges ofoperations depending on the direction of flow of power, and byextension, the operating personality of the wireless power transferdevice 1600 a/1600 b. The various operating set points, modes and/orranges of operation can be stored in memory or in hardware. Eachcomponent of the system (e.g. the inverter-rectifier 1602, TMN 106, andother components) including various controllers, filters, communicationsystems, and/or protection systems can assume a different “operatingpersonality” depending on the direction of power flow.

The wireless power transfer device's bidirectional manager can assign anappropriate personality at system startup and/or during a power flowtransition based on the expected direction of power flow through thewireless power transfer system 1600 as a whole. For example, uponreceipt of a command to switch from one mode of operation for the systemto another, (for example, by an operator interface, and/or userinterface connected to either or all of the controllers, on either orboth sides of the system or off system, such as on a network, the grid,or a mobile device), the bidirectional manager can assign the variouscomponent controllers (e.g., 1304, 1306, 1308, and 1310) a respectiveoperating personality. Each controller can use the assigned operatingpersonality to identify and load appropriate operating processes orsoftware code to control associated components of the wireless powertransfer device 1600 a/1600 b. For instance, when an inverter-rectifiercontroller is assigned an operating personality of an inverter (e.g.,INV), the controller will load software code to generate PWM controlsignal patterns to operate the inverter-rectifier switching elements togenerate AC output signals from a DC input signal. On the other hand,when an inverter-rectifier controller is assigned an operatingpersonality of a rectifier (e.g., REC), the controller will loadsoftware code to generate PWM control signal patterns to operate theinverter-rectifier switching elements to rectify an AC input signal intoa DC output signal.

Furthermore, the bidirectional manager can provide the power demand, thepower flow direction, choose the appropriate software code blocks, andassign personalities to sub-controllers or other controller(s). Thebidirectional manager can determine the errors that are recoverable ornot recoverable, depending on the side the system the controller islocated on, and the operating personality it assumes for components ofthe system. The operational personalities can be assigned based on theexpected power flow direction, e.g. V2G—vehicle-to-grid power flow, orG2V—grid-to-vehicle power flow. Moreover, the bidirectional manager candetermine the time and/or mode for recovery for those errors and/orclear errors when they are recovered so no user intervention is needed.The bidirectional manager can communicate with the user, thecontroller(s) of the other side of the system (e.g., the bidirectionalmanager on the other side of the system).

The bidirectional manager can receive notification of an error from acomponent of the wireless power transfer system and the error messagescan be allocated to other components of the wireless power transfersystem, either directly by the bidirectional manager or after a callbackrequest from the components.

The bidirectional manager can receive communication from components ofthe wireless power transfer system (e.g., via WiFi from components fromthe other side of the system). The bidirectional manager can fulfillcallback requests from components for messages related to the component,or can allocate the message to the relevant components. Thebidirectional manager can control, including dynamically, the privilegesof the components of the wireless power system to receive and send errorand communication messages. The bidirectional manager can be responsiblefor controlling the components of the wireless power transfer systemduring the transition phases, including handling any error conductionarising from the change of power transfer direction (both V2G and G2Vtransitions). For example, the bidirectional manager can oversee turningdown of power, confirm power has fully or partially turned off, andsequence the components of the system to turn on (while assigningpersonalities to the components).

As an example, the bidirectional manager on the GA controller receives acommand to turn on power from idle, the bidirectional manager may assignG2V personality to the various controllers and hardware in the system.Upon receipt of a communication to change the power transfer direction,the bidirectional manager communicates between the GA and VA to changepower transfer direction. The bidirectional manager can be responsiblefor handling any error arising from the change of power transferdirection, including during the power down of the first direction andthe power up of the second direction. When the error is cleared, thebidirectional manager can assign personality to the controller(s), forexample by selecting a subset of instructions from a non-transitorycomputer readable medium, or causing the controller(s) to select thesubset of instructions.

In some implementations, each controller of the system (e.g., adedicated inverter-rectifier processor, or a dedicated TMN processor, ora dedicated transmitter or receiver processor) can contain abidirectional manager. The bidirectional manager can operate as atop-level manager.

Generally, assigning a personality to components/controllers can allowfor modularity, non-redundant parts, code, and memory, allows for fasterand on-the-fly switchover from G2V (grid-to-vehicle power flow) to V2G(vehicle-to-grid power flow) and back.

FIG. 17 depicts flowchart of an exemplary bidirectional control process1700 that can be executed in accordance with implementations of thepresent disclosure. The example process 1700 can be implemented, forexample, by the example wireless power transfer systems disclosedherein. For example, the process 1700 can be executed between abidirectional manager of a GA wireless power transfer device 1600 a anda bidirectional manager of a VA wireless power transfer device 1600 b.Process 1700 shows divided master side operations 1702 and slave side1704 operations. Generally, the master side operations 1702 areperformed by a VA wireless power transfer device 1600 b while the slaveside operations 1704 are performed by a GA wireless power transferdevice 1600 a. For example, the VA (or device-side) wireless powertransfer device 1600 b may generally be coupled to a smaller capacity ormore limited power source or load. Implementing the VA wireless powertransfer device 1600 b as a master device may provide more precisecontrol of the bidirectional control process 1700 to prevent exceedingpossible lower operating limits of the VA side system or itsload/source. In some examples, the example process 1700 can be providedby one or more computer-executable programs executed using one or morecomputing devices, processors, or microcontrollers. For example, theexample process 1700, or portions thereof, can be provided by one ormore programs executed by control circuitry of wireless power transferdevices 1600 a, 1600 b.

The master device initiates a power flow transition within the wirelesspower system. The initiation may be prompted by a user input, or in someimplementations by an automatic power transition determination performedby the master device (1706). For example, the master device candetermine to shift power flow based on various criteria including, butnot limited to, state of charge of a battery, time of day, andavailability and/or demand of grid-power. For example, a VA wirelesspower transfer device 1600 b can be configured to initiate a power flowreversal process when a connected battery is above a threshold chargelevel and a loss of grid power occurs. As another example, a VA wirelesspower transfer device 1600 b can be configured to initiate a power flowreversal process when a connected battery is above a threshold chargelevel and during a preset time of day. For instance, the VA wirelesspower transfer device 1600 b can be configured reverse power flow inorder to provide supplemental power to a home during peak load periodsof a power grid (e.g., periods of high demand and/or high energy pricessuch as evenings). In some implementations, the slave device candetermine when to initiate a power flow transition, but would perform anadditional step of requesting initiation of the power flow transitionfrom the master device.

The master device sends instructions to the slave device to reverse thedirection of power flow (1708). In response to the instructions, theslave device reconfigures for operating in the opposite power flowdirection from its current operations (1710). For example, if the slavedevice was operating as a transmitter it will reconfigure for operationas a receiver. If the slave device was operating as a receiver it willreconfigure for operation as a transmitter. For example, the slavedevice's bidirectional manager can coordinate controller operationswithin the slave device to shut down power flow in the present directionby, for example, securing operation of the inverter-rectifier, shiftingswitches to disconnect a load/power supply (as appropriate), togglingbypass switches to dissipate residual currents within the slave device,or a combination thereof.

The slave device assigns a new operating personality in accordance withthe new power flow direction (1712). For example, the slave device'sbidirectional manager assigns a new operating personality to respectivecontrollers within the slave device as appropriate to the new directionof power flow. The bidirectional power manager can assign the newoperating personality by toggling a flag bit (e.g., TMN_SIDE discussedin more detail below) to indicate operation as a transmitter/inverter oroperation as a receiver/rectifier.

In response to the new operating personality assignment, the variousslave device controllers can reconfigure their respective operations.For example, the controllers can load control algorithms (e.g., softwarecode blocks) to perform operations according to the new power flowdirection. For example, a TMN controller can reset a TMN and loadcontrol code for generating appropriate TMN control signals foroperation in according to the new power flow direction. The TMN may needto adjust set points (e.g., impedance values, impedance adjustment stepsizes, and/or protection schemes) to accommodate power transfer in thenew direction or to prepare for power ramp up in the new direction orboth. For example, power flow in a V2G mode may generally be lower thanin a G2V mode, e.g., due to asymmetries between GA and VA side resonatorcoils and/or discharge constraints on a battery. Consequently, TMNand/or inverter-rectifier set points may be different for operating in aV2G mode vice a G2V mode.

The slave device (e.g., the slave device's inverter controller) cancontrol the inverter-rectifier operation according to the new operatingpersonality (1714). For example, an inverter-rectifier controller canload appropriate algorithms for generating PWM control signals foroperating as an inverter when the slave device is a transmitter andoperating as a rectifier when the slave device is a receiver. Thespecific inverter and rectifier operations are described in more detailbelow in reference to FIGS. 18 and 19 .

The slave device sends a reply to the master device indicating itsreconfiguration status (1716). When the slave device indicates that itsreconfiguration is still in progress or is stalled, the master devicewaits and/or resends an instruction 1708. By the master device waitingfor confirmation that the slave device has completed updating itsoperating personality the process 1700 may provide for safer and morerobust operations. For example, it may prevent the power flow fromcommencing or reversing with mismatched personalities assigned to eitherthe slave or master device. When the slave device indicates that itsreconfiguration is complete, the master device reconfigures foroperating in the opposite power flow direction from its currentoperations (1718). For example, if the master device was operating as atransmitter it will reconfigure for operation as a receiver. If themaster device was operating as a receiver it will reconfigure foroperation as a transmitter. For example, the master device'sbidirectional manager can coordinate controller operations within theslave device to shut down power flow in the present direction by, forexample, securing operation of the inverter-rectifier, shifting switchesto disconnect a load/power supply (as appropriate), toggling bypassswitches to dissipate residual currents within the slave device, or acombination thereof.

The master device assigns a new operating personality in accordance withthe new power flow direction (1720). For example, the master device'sbidirectional manager assigns a new operating personality to respectivecontrollers within the master device as appropriate to the new directionof power flow. The bidirectional (power) manager can assign the newoperating personality by toggling a flag bit (e.g., TMN_SIDE discussedin more detail below) to indicate operation as a transmitter/inverter oroperation as a receiver/rectifier.

In response to the new operating personality assignment, the variousmaster device controllers can reconfigure their respective operations.For example, the controllers can load control algorithms (e.g., softwarecode blocks) to perform operations according to the new power flowdirection. For example, a TMN controller can reset a TMN and loadcontrol code for generating appropriate TMN control signals foroperation in according to the new power flow direction. The TMN may needto adjust set points (e.g., impedance values and/or protection schemes)to accommodate power transfer in the new direction or to prepare forpower ramp up in the new direction or both.

The master device (e.g., the master device's inverter controller) cancontrol the inverter-rectifier operation according to the new operatingpersonality (1722). For example, an inverter-rectifier controller canload appropriate algorithms for generating PWM control signals foroperating as an inverter when the slave device is a transmitter andoperating as a rectifier when the slave device is a receiver. In someimplementations, a TMN controller in the master device can control theTMN according to the new operating personality. For example, a TMNcontroller on the master device can load appropriate control algorithmsfor generating TMN adjustment signals for operating as a load coupledTMN in a first direction, or a power supply coupled TMN in a seconddirection.

FIG. 18 depicts a schematic 1800 of an exemplary inverter-rectifier 1602and a timing diagram 1802 illustrating operation of theinverter-rectifier in an inverter operating mode. The schematic 1800shows a phase shifted full-bridge inverter. The inverter bridge circuituses active switching elements Q1, Q2, Q3, and Q4, which can be, forexample, MOSFETSs, transistors, FETs, IGBTs, etc.

The timing diagram 1802 illustrates the driving signal pattern for theswitches Q1, Q2, Q3, and Q4. The switches are grouped into two legs; LegA (Q1, Q3) and Leg B (Q2, Q4). The corresponding switches in each legare alternately switched on and off by respective PWM control signals.On time and off time, for each gate drive signal G1, G2, G3, and G4 areshown. The dead time t_(d) shown is when both gate drivers of the sameleg are off. The off time may be larger than the on time for eachdriving signal in a period Ts.

The delay time tps between Leg A (Q1 and Q3) and Leg B (Q2 and Q4), whenexpressed in degrees, is known as the phase-shift angle and is a meansfor adjusting the overall power sourced by the inverter-rectifier whenoperating as an inverter. At start-up, output power V_(AB)(t) frominverter-rectifier terminals V_(A) and V_(B), can have an 11% duty cycle(leg phase-shift angle θps=20 degrees). At max power, V_(AB)(t) can beat a 100% duty cycle (leg phase θps=180 degrees). Total power output iscontrolled by adjusting the delay time t_(PS) between the Leg A and LegB PWM signals.

Although a full bridge inverter is shown, in some implementations theinverter-rectifier switches can be arranged in a half-bridgeconfiguration. In some implementations, the inverter-rectifier canimplement zero-voltage switching operations to ensure the switches areoperated when the voltage across them is zero or near-zero.

FIG. 19 depicts a schematic 1900 of an exemplary inverter-rectifier anda timing diagram 1902 illustrating operation of the inverter-rectifier1602 in a rectifier operating mode. FIG. 19 illustrates a synchronousrectifier operation utilizing the same switches as shown in FIG. 18 .The gate drive signals (G1, G2, G3, G4) corresponding to respectiveswitches (Q1, Q2, Q3, Q4) are shown in the timing diagram 1902. Althoughzero current switching operation is shown, zero-voltage switching (ZVS)naturally follows the operation and can be used in some implementations.However, ZVS switching in active rectification mode is not shown infigures.

The synchronous rectifier can receive the zero-crossing of the I3 scurrent (shown as I3 d or I3 s in FIG. 16 ) and creates the timing ofthe synchronous rectification (zero current switching) as shown intiming diagram 1902. In the rectifier mode, the inverter-rectifier 1602rectifies an AC input signal into a DC output signal by alternatelyswitching on corresponding pairs of switches (Q1/Q4 and Q2/Q3). Forexample, the inverter-rectifier controller (e.g., inverter/protectionand control circuitry 176) can receive 13 d or 13 s current and/or phasemeasurements from a current or phase sensor such as phase sensor 142 orcurrent sensor 150 illustrated in FIGS. 1C, 1D, 5A, and 6A. The switchesQ1, Q2, Q3, and Q4 can be turned off at the zero current (or near zerocurrent) of the input to the inverter-rectifier 1602, and an appropriatetime delay t_(d) may be permitted to lapse before operating the nextpair of switches (e.g., Q1 and Q4 or Q2 and Q3). This can prevent powerlosses within the switch. In some implementations, the time delay may beadjusted by the system as needed.

In some implementations, during a startup, the inverter-rectifier doesnot begin does not begin switching until the measured input power isabove a threshold value that ensures continuous conduction of the 13current. The threshold value can be, e.g., between 2 kW and 4 kW, and/orbetween 20-40% of a target power. During the low power operations belowthe threshold input power value, the input AC signal may be noisy,potentially resulting in inaccurate zero-crossing detections andpossibly large transients for imprecise switching. For example, the 13current that is used to generate the PWM synchronization may bediscontinuous and noisy resulting in inaccurate zero-crossing detectionsand possibly large transients or even in a destructive shorting of thepower stage. Instead, rectification can be performed passively whenpower is below the threshold value by conduction through the body-diodesof the switches. In such implementations, the switching operationsperformed above the threshold input power value can be considered anactive rectification mode and the body-diode conduction below thethreshold input power value can be considered a passive rectificationmode.

FIG. 20 depicts a flowchart of exemplary protection operations 2000 thatcan be executed in accordance with implementations of the presentdisclosure. The example operations 2000 can be implemented, for example,by the example wireless power transfer devices (e.g., 1600 a, 1600 b)disclosed herein. For example, the operations 2000 can be executed bycontrol circuitry of a wireless power transfer device. For example, theoperations 2000 can be executed by an inverter-rectifier controller andinverter protection circuitry such as the logic circuits shown in FIG.22A. In some implementations, the operations 2000 can be executed in adifferent order than that shown in FIG. 20 . Furthermore, the protectionoperations 2000 will be described in reference to FIGS. 20-22B.

FIG. 21 is a diagram 2100 of a bidirectional wireless power transferdevice that illustrates an arrangement of fault sensing circuits.Diagram 2100 illustrates the locations at which various fault signalsdescribed below are measured in the wireless power transfer device. Thefault signals illustrated include OV_CMD, VOUT_I, VOUT_V, OVP, WIFI_FLT,and TMN_FLT. FIG. 22A is a block diagram 2200 of exemplary protectionlogic for a bidirectional wireless power transfer device and FIG. 22Billustrates logic truth tables associated with the exemplary protectionlogic shown in FIG. 22A.

In FIG. 22A the logic circuitry 2210 evaluates faults during anoperating personality as an inverter, and logic circuitry 2212 evaluatesfaults during an operating personality as a rectifier. The logiccircuitry 2220 enables particular protective actions specific to arectifier operating personality. The illustrated protection logic isexemplary, and may be simplified or further expanded, and may beimplemented in hardware or software. Logic can be active high or activelow, and the outputs of previous logic can be appropriately negated.

The logic circuitry 2210 evaluates various system faults includingDESAT_flg, UVLO_flg WIFI_FLT, TMN_FLT, and OC_FLT. DESAT_flg andUVLO_flg are flags that are used in some implementations to indicateproper operation of the rectifier-inverter switches. For example, theymay indicate a desaturation condition in an IGBT switch. WIFI_FLTindicates that a WiFi fault has occurred. For example, if a fault occurson one wireless power transfer device (e.g. a receiver) it maycommunicate the fault to another device (e.g., the transmitter) to allowthe device to execute appropriate actions to maintain the safety of thesystem as a whole. TMN_FLT is discussed above, and indicates that afault has occurred at the TMN (e.g., a TMN over and/or under currentfault). OC_FLT indicates that an over current condition has occurred atthe inverter-rectifier. The logic circuitry 2220 generally evaluates thesame faults as logic circuitry 2210, but also may include an additionalfault signal; OV_FLT. OV_FLT may indicate an over voltage fault atwireless power device. For example, when operating as a rectifier, theOV_FLT may serve as an indication of a load disconnect fault, asdiscussed below.

The control circuitry detects a fault condition (2002). For example, thecontrol circuitry receives one of the fault signals shown in FIGS. 21,22A, and 22B. For example, Truth Table 2 of FIG. 22B shows the logiccombinations that generate an inverter enable signal (INV_ENBL). Whenthe INV_ENBL signal is high the PWM signals are passed through the NANDgate 2202 in FIG. 22A. However, if any of the faults in Truth Table 2are detected (e.g., the fault signal goes low), the INV_ENBL signals isdisabled (low), indicating the existence of a fault condition.

The control circuitry identifies an operating personality and a hardwareconfiguration of the wireless power transfer device (2004). For example,the particular protective action that the control circuitry will performis executed based on the operating personality and hardwareconfiguration of the wireless power transfer device. As discussed above,the operating personality can be indicated by a flag such as theTMN_SIDE flag shown in FIG. 22A and the truth tables in FIG. 22B. TheTMN_SIDE flag indicates whether the wireless power transfer device isoperating as a receiver or a transmitter. Referring to Truth Tables 1and 4, the value of TMN_SIDE corresponds to an operating personality ofINV (e.g., operation as an inverter and a transmitter) when the value is0 and an operating personality of REC (e.g., operation as a rectifierand a receiver) when the value is 1. A hardware configuration refers toa flag that indicates whether the control circuitry is controlling awireless power transfer device configured as a GA side device (e.g., agrid-connected system) or a VA side device (e.g., a device-connectedsystem). The hardware configuration indicates to the control circuitrywhich protective actions can be executed based on the operatingconfigurations and limitations of the hardware. For example, GA sideresonators and TMNs can be configured differently from VA sideresonators and TMNs. Consequently, GA side resonators and TMNs may havedifferent (e.g., generally higher) operating limits than VA sidecomponents, and different protective actions may be required. Referringto Truth Tables 1 and 4, the value of INVREC_SIDE indicates that thewireless power transfer device is configured as a GA side device whenthe value is 0 and that the wireless power transfer device is configuredas a VA side device when the value is 1.

The control circuitry identifies protection operations for protectingthe wireless power transfer device from the fault condition based on theidentified operating personality and hardware configuration (2006). Thecontrol circuitry controls the operations of the wireless power transferdevice in accordance with the protection operations (2008). For example,as indicated by Truth Table 1, if the wireless power transfer device isoperating as an inverter (e.g., a power transmitter) (TMN_SIDE=0) and isconfigured as a either a GA or a VA (INVREC_SIDE=0 or 1) the PWM controlsignals for the inverter-rectifier will be overridden and force to zeroif any fault occurs that disables INV_ENBL, thereby, shutting down theinverter-rectifier. In addition, a component of the IMN 103 can beshorted to dissipate residual current in the resonator coil. Forexample, switches SW1 1608 of FIG. 16 can be closed to dissipate anyresidual resonator current. In some implementations, if the hardwareconfiguration of the wireless power transfer device indicates that thedevice is configured as a GA side device and the operating personalityis an inverter (power transmitter) the protective operations can furtherinclude switching in a resistor configured to dissipate excess powerfrom the inverter-rectifier. For example, the control circuitry canclose switch SW2 1610 to dissipate excess power from the power source1604 through resistor R1 1612 shown in FIG. 16 . In someimplementations, the resistor may only be switched in for certain faulttypes. For example, if the device is configured as a GA and operating asan inverter the resistor may be switched in for an over current fault.If the device is configured as a GA and operating as a rectifier theresistor may be switched in for an over voltage fault.

If the operating personality indicates that the wireless power transferdevice is operating as a rectifier (power receiver) (e.g., TMN_SIDE=1)and a fault occurs (e.g., as indicated by INV_ENBL falling low in TruthTable 1) the control circuitry can shutdown the inverter-rectifier byoverriding the PWM control signals. In some implementations, the controlcircuitry can also short a component of the matching network todissipate residual current in the resonator coil by, for example,closing switches SW1 1608 of FIG. 16 .

As indicated by Truth Tables 1 and 4, if the operating personalityindicates that the wireless power transfer device is operating as arectifier (power receiver) (e.g., TMN_SIDE=1) and the hardwareconfiguration is as a VA (INVREC_SIDE=1) when a fault occurs (e.g., asindicated by REC_FLTS going high) the control circuitry can shutdown theinverter-rectifier by overriding the PWM control signals to short the ACside of the inverter-rectifier (e.g., gate drive signals G3, G4=1). Forexample, FIG. 23 shows a series of diagrams 2300 depicting the operationof the inverter-rectifier in response to a load disconnect when assigneda rectifier operating personality. The diagrams 2300 illustrate theswitching of the grid tied inverter if there is a grid disconnect, orthe switching of the vehicle inverter if there is a battery disconnect(when battery is the load) is shown. In diagram 2302 theinverter-rectifier is operating normally as a rectifier. In diagram 2304the load disconnect occurs routing current through capacitor Cdc. Theoutput capacitor (decoupling capacitor Cdc) operates as theovervoltage/load disconnect sensor as described above, however it isunderstood that other sensing means can be employed. As discussed above,upon detection of the load disconnect and identification that theinverter-rectifier is operating as a rectifier and has a hardwareconfiguration as a VA, the control circuitry shorts the AC side of theinverter by turning transistors Q3 and Q4 on, and open circuits the DCside by turning transistors Q1 and Q2 off (diagram 2306).

In some implementations, shorting the AC side of the inverter-rectifierin response to a VA side fault (such as a load disconnect) duringoperation as a rectifier (power receiver) causes a corresponding faultto occur on the associated GA side device by initiating overcurrentand/or overvoltage transients on the GA side device, as discussed abovein reference to FIG. 14 . Initiating a GA side shutdown in this mannermay provide a quicker system wide fault response rather than passingfault codes through the communication link. For example, if thecommunication link fails or experiences a slow connection (e.g.,increased noise or bit errors).

In some implementations, the assertion of REC_FLTS also causes theOC_CMD signal to be asserted. This signal drives the switch 2102 in FIG.21 , which switches in a resistor to aid in power dissipation. Thesignal may also directly drive switches which short components of theimpedance matching network, such as SW1 1608 of FIG. 16 .

In some implementations, in the event of a grid-disconnect (e.g., whenthe hardware configuration is GA) the control circuitry can shutdown theinverter by turning all the transistors Q1-Q4 off.

In some implementations, the wireless power transfer devices can includea load disconnect sensor. For example, a load disconnect can be detectedby an over voltage or an under current condition at the output (loadside) of an inverter-rectifier when operating as a rectifier. Forexample, a VA side device operating as a receiver may detect a loaddisconnect by receiving an over voltage fault, an undercurrent fault, orboth. In response, control and protection circuitry in the VA sidedevice can shutdown the inverter-rectifier by shorting two or morerectifier protection switches (e.g., Q3 and Q4 of FIG. 21 ). Each of theprotection switches may also be coupled to a diode to include abody-diode. The control and protection circuitry in the VA side devicecan short a protection switch coupled to a TMN to short (and protect)the TMN. Shorting the inverter-rectifier may cause a correspondingovercurrent transient on the GA side device. In response to theovercurrent fault, the GA side device (operating as a transmitter) canshutdown its inverter-rectifier and short its TMN. The current andvoltage response to a load disconnect event are described in more detailabove in reference to FIG. 14 .

In reference to FIG. 16 , in some implementations, the resonator coil L1s may be designed to accommodate for higher current during loaddisconnect conditions. However, methods such as shorting parallel TMNelements (such as C2) and/or switching in a resistor (such as R1), maybe important in implementations where excess coil current/voltage maycause arcing or heating at the coil L1 s.

In some implementations, a communication link (e.g., a WiFi link) can beused to protect the system from failure. For example, if a loaddisconnect occurs the receiver can inform the transmitter of the faultvia the communication link. During low power operation the shutdownoperation of the receiver as described above may not induce a largeenough transient current in the transmitter to produce a correspondingover current fault. Therefore, the fault communicated through thecommunication link may serve to trigger protective action by thetransmitter. For example, the receiver side, upon detection of a fault,such as a load disconnect (over voltage), would communicate the faultinformation to the transmitter side via the WiFi or other out-of-bandcommunication requiring the source side inverter to turn-off. In themeantime until the transmitter-side inverter turns off, protectionmechanisms on the receiver side such as switching in resistor R1 and orshorting components of the TMN and or IMN can allow for reducing of coilcurrents.

In some implementations, upon detection of an overvoltage condition(e.g. because of load disconnect), upon detecting V(v_bus+) rising inthe output capacitor, the resistor R1 parallel with the load, can beswitched in, and/or the capacitor C2 in parallel with the load can beshorted in by the controller. Switching in the parallel resistor R1 canallow some or all the current to circulate in the resistor, and shortingthe capacitor C2 can reduce excess coil current on the load-side coil.This can ensure the system is safe until an error message containinginformation regarding the fault can be communicated from the load sideto the source side. The error message can include requiring the sourceside inverter to turn-off, or the error message can be interpreted bythe source side inverter as a command to turn off. In someimplementations (e.g., for an 11 kW system), the resistor R1 can besized according to the power rating of the system and the communicationchannel latency (from the load side to the source side) time, and/or thetime the source side takes to shut down power.

In some implementations, a load short fault can be detected by an undervoltage fault at the output of the rectifier. For example, a VA sidedevice operating as a receiver (e.g., inverter-rectifier operating as arectifier) can detect a load short condition when the output voltagedrops at the rectifier output. In response, the control and protectioncircuitry of the VA side device can short a protection switch coupled toa TMN on the VA side device. This may cause a corresponding currenttransient in the GA side device operating as a transmitter. In response,the control and protection circuitry on the GA side device may detect anovercurrent condition. In response, the control and protection circuitryon the GA side device can short a protection switch coupled to a TMN onthe GA side device

In this disclosure, certain circuit or system components such ascapacitors, inductors, resistors, are referred to as circuit“components” or “elements.” The disclosure also refers to series andparallel combinations of these components or elements as elements,networks, topologies, circuits, and the like. More generally, however,where a single component or a specific network of components isdescribed herein, it should be understood that alternativeimplementations may include networks for elements, alternative networks,and/or the like.

As used herein, the term “direct connection” or “directly connected,”refers to a direct connection between two elements where the elementsare connected with no intervening active elements between them. The term“electrically connected” or “electrical connection,” refers to anelectrical connection between two elements where the elements areconnected such that the elements have a common potential. In addition, aconnection between a first component and a terminal of a secondcomponent means that there is a path between the first component and theterminal that does not pass through the second component.

As used herein, the term “coupled” when referring to circuit or systemcomponents is used to describe an appropriate, wired or wireless, director indirect, connection between one or more components through whichinformation or signals can be passed from one component to another.Furthermore, the term “coupled” when used in reference to electriccircuit components or electric circuits generally refers to an“electrical connection” unless otherwise stated.

Implementations of the subject matter and the operations described inthis specification can be realized in digital electronic circuitry, orin computer software, firmware, or hardware, including the structuresdisclosed in this specification and their structural equivalents, or incombinations of one or more of them. Implementations of the subjectmatter described in this specification can be realized using one or morecomputer programs, i.e., one or more modules of computer programinstructions, encoded on computer storage medium for execution by, or tocontrol the operation of, data processing apparatus. Alternatively or inaddition, the program instructions can be encoded on an artificiallygenerated propagated signal, e.g., a machine-generated electrical,optical, or electromagnetic signal that is generated to encodeinformation for transmission to suitable receiver apparatus forexecution by a data processing apparatus. A computer storage medium canbe, or be included in, a computer-readable storage device, acomputer-readable storage substrate, a random or serial access memoryarray or device, or a combination of one or more of them. Moreover,while a computer storage medium is not a propagated signal; a computerstorage medium can be a source or destination of computer programinstructions encoded in an artificially generated propagated signal. Thecomputer storage medium can also be, or be included in, one or moreseparate physical components or media (e.g., multiple CDs, disks, orother storage devices).

The operations described in this specification can be implemented asoperations performed by a data processing apparatus on data stored onone or more computer-readable storage devices or received from othersources.

The term “data processing apparatus” encompasses all kinds of apparatus,devices, and machines for processing data, including by way of example aprogrammable processor, a computer, a system on a chip, or multipleones, or combinations, of the foregoing. The apparatus can includespecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) or an ASIC (application-specific integrated circuit). Theapparatus can also include, in addition to hardware, code that createsan execution environment for the computer program in question, e.g.,code that constitutes processor firmware, a protocol stack, a databasemanagement system, an operating system, a cross-platform runtimeenvironment, a virtual machine, or a combination of one or more of them.The apparatus and execution environment can realize various differentcomputing model infrastructures, such as web services, distributedcomputing and grid computing infrastructures.

A computer program (also known as a program, software, softwareapplication, script, or code) can be written in any form of programminglanguage, including compiled or interpreted languages, declarative orprocedural languages, and it can be deployed in any form, including as astand-alone program or as a module, component, subroutine, object, orother unit suitable for use in a computing environment. A computerprogram may, but need not, correspond to a file in a file system. Aprogram can be stored in a portion of a file that holds other programsor data (e.g., one or more scripts stored in a markup languagedocument), in a single file dedicated to the program in question, or inmultiple coordinated files (e.g., files that store one or more modules,sub-programs, or portions of code). A computer program can be deployedto be executed on one computer or on multiple computers that are locatedat one site or distributed across multiple sites and interconnected by acommunication network.

The processes and logic flows described in this specification can beperformed by one or more programmable processors executing one or morecomputer programs to perform actions by operating on input data andgenerating output. The processes and logic flows can also be performedby, and apparatus can also be implemented as, special purpose logiccircuitry, e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only memory ora random access memory or both. Elements of a computer can include aprocessor for performing actions in accordance with instructions and oneor more memory devices for storing instructions and data. Generally, acomputer will also include, or be operatively coupled to receive datafrom or transfer data to, or both, one or more mass storage devices forstoring data, e.g., magnetic, magneto-optical disks, or optical disks.However, a computer need not have such devices. Moreover, a computer canbe embedded in another device, e.g., a wireless power transmitter orreceiver or a wirelessly charged or powered device such as a vehicle, amobile telephone, a personal digital assistant (PDA), a mobile audio orvideo player, a game console, or a Global Positioning System (GPS)receiver, to name just a few. Devices suitable for storing computerprogram instructions and data include all forms of non-volatile memory,media and memory devices, including by way of example semiconductormemory devices, e.g., EPROM, EEPROM, and flash memory devices; magneticdisks, e.g., internal hard disks or removable disks; magneto-opticaldisks; and CD-ROM and DVD-ROM disks. The processor and the memory can besupplemented by, or incorporated in, special purpose logic circuitry.

While this specification contains many specific implementation details,these should not be construed as limitations on the scope of anyimplementation of the present disclosure or of what may be claimed, butrather as descriptions of features specific to example implementations.Certain features that are described in this specification in the contextof separate implementations can also be implemented in combination in asingle implementation. Conversely, various features that are describedin the context of a single implementation can also be implemented inmultiple implementations separately or in any suitable sub-combination.Moreover, although features may be described above as acting in certaincombinations and even initially claimed as such, one or more featuresfrom a claimed combination can in some cases be excised from thecombination, and the claimed combination may be directed to asub-combination or variation of a sub-combination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. In certain circumstances, multitasking and parallel processingmay be advantageous. Moreover, the separation of various systemcomponents in the implementations described above should not beunderstood as requiring such separation in all implementations, and itshould be understood that the described program components and systemscan generally be integrated together in a single software product orpackaged into multiple software products.

What is claimed is:
 1. A method of operating a bidirectional wirelesspower transfer system, the method comprising: receiving, by a slavewireless power transfer device from a master wireless power transferdevice, instructions to reverse a direction of power flow between theslave wireless power transfer device and the master wireless powertransfer device; in response to the instructions: assigning a wirelesspower receiver operating personality to the slave wireless powertransfer device; and controlling operation of an inverter-rectifier ofthe slave wireless power transfer device according to the wireless powerreceiver operating personality, wherein controlling operation of theinverter-rectifier comprises: in response to a power at theinverter-rectifier being less than a threshold value, operating theinverter-rectifier in a passive rectifier mode; and in response to thepower at the inverter-rectifier being greater than a threshold value,generating pulse width modulation (PWM) control signals for operatingthe inverter-rectifier in an active rectification mode; and sending, tothe master wireless power transfer device, an indication that the slavewireless power transfer device has reconfigured to operate as a wirelesspower receiver.
 2. The method of claim 1, wherein controlling operationof the inverter-rectifier comprises generating pulse width modulation(PWM) control signals for operating the inverter-rectifier as arectifier.
 3. The method of claim 1, wherein the PWM control signalsalternately turn on corresponding pairs of transistors in theinverter-rectifier to generate a DC output signal.
 4. The method ofclaim 1, wherein the PWM control signals alternately turn oncorresponding pairs of transistors in the inverter-rectifier in responseto detecting a zero current condition at an input to theinverter-rectifier.
 5. The method of claim 1, further comprising inresponse to the indication, resetting a tunable matching network of themaster wireless power transfer device and controlling operation of thetunable matching network according to an assigned operating personality.6. The method of claim 1, wherein the master wireless power transferdevice is coupled to a vehicle and the slave wireless power transferdevice is coupled to a power grid.
 7. The method of claim 1, whereinassigning the wireless power receiver operating personality to the slavewireless power transfer device comprises toggling an operatingpersonality flag bit, wherein a value of the operating personality flagbit controls one or more protective actions in the event of an operatingfault.
 8. A non-transitory computer readable storage medium storinginstructions that, when executed by at least one processor, cause the atleast one processor to perform operations comprising: receiving, by aslave wireless power transfer device from a master wireless powertransfer device, instructions to reverse a direction of power flowbetween the slave wireless power transfer device and the master wirelesspower transfer device; in response to the instructions: assigning awireless power receiver operating personality to the slave wirelesspower transfer device; and controlling operation of aninverter-rectifier of the slave wireless power transfer device accordingto the wireless power receiver operating personality, whereincontrolling operation of the inverter-rectifier comprises: in responseto a power at the inverter-rectifier being less than a threshold value,operating the inverter-rectifier in a passive rectifier mode; and inresponse to the power at the inverter-rectifier being greater than athreshold value, generating pulse width modulation (PWM) control signalsfor operating the inverter-rectifier in an active rectification mode;and sending, to the master wireless power transfer device, an indicationthat the slave wireless power transfer device has reconfigured tooperate as a wireless power receiver.
 9. The medium of claim 8, whereincontrolling operation of the inverter-rectifier comprises generatingpulse width modulation (PWM) control signals for operating theinverter-rectifier as a rectifier.
 10. The medium of claim 8, whereinthe PWM control signals alternately turn on corresponding pairs oftransistors in the inverter-rectifier to generate a DC output signal.11. The medium of claim 8, wherein the PWM control signals alternatelyturn on corresponding pairs of transistors in the inverter-rectifier inresponse to detecting a zero current condition at an input to theinverter-rectifier.
 12. The medium of claim 8, further comprising inresponse to the indication, resetting a tunable matching network of themaster wireless power transfer device and controlling operation of thetunable matching network according to an assigned operating personality.13. The medium of claim 8, wherein the master wireless power transferdevice is coupled to a vehicle and the slave wireless power transferdevice is coupled to a power grid.
 14. The medium of claim 8, whereinassigning the wireless power receiver operating personality to the slavewireless power transfer device comprises toggling an operatingpersonality flag bit, wherein a value of the operating personality flagbit controls one or more protective actions in the event of an operatingfault.
 15. A wireless power transfer device comprising: at least oneprocessor; and a data store coupled to the at least one processor havinginstructions stored thereon which, when executed by the at least oneprocessor, causes the at least one processor to perform operationscomprising: receiving, by the wireless power transfer device from amaster wireless power transfer device, instructions to reverse adirection of power flow between the wireless power transfer device andthe master wireless power transfer device; in response to theinstructions: assigning a wireless power receiver operating personalityto the wireless power transfer device; and controlling operation of aninverter-rectifier of the wireless power transfer device according tothe wireless power receiver operating personality, wherein controllingoperation of the inverter-rectifier comprises: in response to a power atthe inverter-rectifier being less than a threshold value, operating theinverter-rectifier in a passive rectifier mode; and in response to thepower at the inverter-rectifier being greater than a threshold value,generating pulse width modulation (PWM) control signals for operatingthe inverter-rectifier in an active rectification mode; and sending, tothe master wireless power transfer device, an indication that thewireless power transfer device has reconfigured to operate as a wirelesspower receiver.
 16. The device of claim 15, wherein controllingoperation of the inverter-rectifier comprises generating pulse widthmodulation (PWM) control signals for operating the inverter-rectifier asa rectifier.
 17. The device of claim 15, wherein the PWM control signalsalternately turn on corresponding pairs of transistors in theinverter-rectifier to generate a DC output signal.
 18. The device ofclaim 15, wherein the PWM control signals alternately turn oncorresponding pairs of transistors in the inverter-rectifier in responseto detecting a zero current condition at an input to theinverter-rectifier.
 19. The device of claim 15, further comprising inresponse to the indication, resetting a tunable matching network of themaster wireless power transfer device and controlling operation of thetunable matching network according to an assigned operating personality.20. The device of claim 15, wherein the master wireless power transferdevice is coupled to a vehicle and the wireless power transfer device iscoupled to a power grid.